updates filter to get translation source

[sheralim012]

Fixes #547

steps to reproduce the issue

• create locales L1, L2, L3
• create a page P1 in locale L1
• translate page P1 to locale L2 (let's say the newly translated page is P1')
• translate page P1' to locale L3 (let's say the newly translated page is P1'')
• you will be redirected to edit page with error MultipleObjectsReturned - get() returned more than one TranslationSource -- it returned 2!

observations

• above-mentioned scenario creates 2 translation sources with same object_id, and spectific_content_type_id but from different locales
• "convert to alias" buttons' logic (finding the source of translation) is dependent on these 2 fields but these 2 fields alone can't uniquely identify the translation source (hence the error - multiple objects returned)

solution

the combination of object_id, spectific_content_type_id, and translations__target_locale_id can uniquely identify the translation source

Let me know if I missed something.

[zerolab]

Hey @sheralim012, thank you for this!
Any chance you could add some tests?

[codecov-commenter]

Codecov Report

Merging #578 (047efd2) into main (7d6278c) will increase coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #578      +/-   ##
==========================================
+ Coverage   91.44%   91.55%   +0.11%     
==========================================
  Files          47       47              
  Lines        3894     3898       +4     
  Branches      591      592       +1     
==========================================
+ Hits         3561     3569       +8     
+ Misses        192      185       -7     
- Partials      141      144       +3     

Impacted Files	Coverage Δ
wagtail_localize/views/convert.py	71.62% <ø> (+1.35%)	⬆️
wagtail_localize/views/edit_translation.py	85.44% <ø> (+1.53%)	⬆️
wagtail_localize/wagtail_hooks.py	80.11% <ø> (ø)
wagtail_localize/components.py	82.69% <0.00%> (-1.93%)	⬇️
wagtail_localize/compat.py	51.85% <0.00%> (-0.33%)	⬇️
wagtail_localize/models.py	95.57% <0.00%> (-0.15%)	⬇️

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[sheralim012]

@zerolab I have added the test cases.
Could you review it now?

[zerolab]

Thank you for this, @sheralim012. Tested locally and works well.