Do not start the asynchronous task manager in tests

[replaceafill]

This avoids a runtime warning shown intermittently when tests are executed:

WARNING   2024-10-02 08:31:10  locations.models.async_manager:async_manager:_watchdog:61:  Failure in watchdog thread: Database access not allowed, use the "django_db" mark, or the "db" or "transactional_db" fixtures to enable it.
Traceback (most recent call last):
  File "/src/storage_service/locations/models/async_manager.py", line 59, in _watchdog
    AsyncManager._watchdog_loop()
  File "/src/storage_service/locations/models/async_manager.py", line 72, in _watchdog_loop
    Async.objects.filter(
  File "/pyenv/data/versions/3.9.20/lib/python3.9/site-packages/django/db/models/query.py", line 1148, in delete
    deleted, _rows_count = collector.delete()
  File "/pyenv/data/versions/3.9.20/lib/python3.9/site-packages/django/db/models/deletion.py", line 459, in delete
    with transaction.atomic(using=self.using, savepoint=False):
  File "/pyenv/data/versions/3.9.20/lib/python3.9/site-packages/django/db/transaction.py", line 198, in __enter__
    if not connection.get_autocommit():
  File "/pyenv/data/versions/3.9.20/lib/python3.9/site-packages/django/db/backends/base/base.py", line 464, in get_autocommit
    self.ensure_connection()
  File "/pyenv/data/versions/3.9.20/lib/python3.9/site-packages/pytest_django/plugin.py", line 813, in _blocking_wrapper
    raise RuntimeError(
RuntimeError: Database access not allowed, use the "django_db" mark, or the "db" or "transactional_db" fixtures to enable it.

[Dhwaniartefact]

LGTM!