fix: 5247 - now "unselect"ing for the correct language

[monsieurtanuki]

What

• We passed the correct language to the "unselect" task, but we didn't use this language as "the task" language.
• As a consequence, we used the default language and unselected the wrong image.
• Now it's fixed.

Fixes bug(s)

• Fixes: The wrong picture is deleted when deleting a picture in a "not-default" language on the app #5247

Impacted file

• background_task_unselect.dart: use of explicit language instead of default language.

[monsieurtanuki]

@jusdekiwi ping

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 8.61%. Comparing base (4d9c7fc) to head (45e4d38).
Report is 121 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #5266      +/-   ##
==========================================
- Coverage     9.54%   8.61%   -0.94%     
==========================================
  Files          325     329       +4     
  Lines        16411   16736     +325     
==========================================
- Hits          1567    1441     -126     
- Misses       14844   15295     +451     

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[jusdekiwi]

@monsieurtanuki brilliant! Looking forward to testing it! Thank you :D