Prevent unique constraint saving errors.

[rtibbles]

Summary

While doing some local testing to attempt to resolve #11895 (comment) I noticed an unrelated error, where content download removal request processing was causing breakage.

References

Traceback:

ERROR    2024-02-19 16:32:28,147 Job 78af46f9c4724ad7a926a96cc829cac4 raised an exception: Traceback (most recent call last):
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/backends/sqlite3/base.py", line 328, in execute
    return Database.Cursor.execute(self, query, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
sqlite3.IntegrityError: UNIQUE constraint failed: content_contentrequest.type, content_contentrequest.source_model, content_contentrequest.source_id, content_contentrequest.contentnode_id

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/richard/github/kolibri/kolibri/core/tasks/job.py", line 329, in execute
    result = func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/github/kolibri/kolibri/core/tasks/registry.py", line 238, in __call__
    return self.func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/github/kolibri/kolibri/core/content/tasks.py", line 403, in automatic_resource_import
    process_content_requests()
  File "/home/richard/github/kolibri/kolibri/core/content/utils/content_request.py", line 505, in process_content_requests
    _process_content_requests(incomplete_downloads)
  File "/home/richard/github/kolibri/kolibri/core/content/utils/content_request.py", line 733, in _process_content_requests
    process_user_downloads_for_removal()
  File "/home/richard/github/kolibri/kolibri/core/content/utils/content_request.py", line 896, in process_user_downloads_for_removal
    user_download_removal.save()
  File "/home/richard/github/kolibri/kolibri/core/content/models.py", line 505, in save
    return super(ContentRequest, self).save(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/models/base.py", line 807, in save
    self.save_base(using=using, force_insert=force_insert,
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/models/base.py", line 838, in save_base
    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/models/base.py", line 924, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/models/base.py", line 962, in _do_insert
    return manager._insert([self], fields=fields, return_id=update_pk,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/models/query.py", line 1079, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/models/sql/compiler.py", line 1112, in execute_sql
    cursor.execute(sql, params)
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/backends/utils.py", line 60, in execute
    with self.db.wrap_database_errors:
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/utils.py", line 94, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/utils/six.py", line 685, in reraise
    raise value.with_traceback(tb)
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/richard/.virtualenvs/kolibripy3.11/lib/python3.11/site-packages/django/db/backends/sqlite3/base.py", line 328, in execute
    return Database.Cursor.execute(self, query, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
django.db.utils.IntegrityError: UNIQUE constraint failed: content_contentrequest.type, content_contentrequest.source_model, content_contentrequest.source_id, content_contentrequest.contentnode_id

Reviewer guidance

Prevents the above error by doing an update_or_create call instead.

---

Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
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• Critical and brittle code paths are covered by unit tests

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Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.16.0rc2.dev0_git.2.g88921370.pex
Windows Installer (EXE)	kolibri-0.16.0rc2.dev0+git.2.g88921370-unsigned.exe
Debian Package	kolibri_0.16.0rc2.dev0+git.2.g88921370-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0rc2.dev0+git.2.g88921370-0.4.0.dmg
Android Package (APK)	kolibri-0.16.0rc2.dev0+git.2.g88921370-0.1.0-debug.apk
TAR file	kolibri-0.16.0rc2.dev0+git.2.g88921370.tar.gz
WHL file	kolibri-0.16.0rc2.dev0+git.2.g88921370-py2.py3-none-any.whl

[bjester]

LGTM after slack discussion :)