fix: resolve test errors and deprecation warnings

[slowsage]

Description

Installing minigalaxy-git on arch fails (paru -S minigalaxy-git) with errors and warnings:

__________________________________________ ERROR collecting tests/test_ui_library.py __________________________________________
ImportError while importing test module '/home/sridhar/.cache/paru/clone/minigalaxy-git/src/minigalaxy/tests/test_ui_library.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/lib/python3.14/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tests/test_ui_library.py:9: in <module>
    from MockGiRepository import MockGiRepository
E   ModuleNotFoundError: No module named 'MockGiRepository'
__________________________________________ ERROR collecting tests/test_ui_window.py ___________________________________________
ImportError while importing test module '/home/sridhar/.cache/paru/clone/minigalaxy-git/src/minigalaxy/tests/test_ui_window.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/lib/python3.14/importlib/__init__.py:88: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
tests/test_ui_window.py:6: in <module>
    from MockGiRepository import MockGiRepository
E   ModuleNotFoundError: No module named 'MockGiRepository'
====================================================== warnings summary =======================================================
minigalaxy/api.py:235
  /home/sridhar/.cache/paru/clone/minigalaxy-git/src/minigalaxy/minigalaxy/api.py:235: SyntaxWarning: 'return' in a 'finally' block
    return result

minigalaxy/translation.py:32
  /home/sridhar/.cache/paru/clone/minigalaxy-git/src/minigalaxy/minigalaxy/translation.py:32: DeprecationWarning: 'locale.getdefaultlocale' is deprecated and slated for removal in Python 3.15. Use setlocale(), getencoding() and getlocale() instead.
    default_locale = locale.getdefaultlocale()[0]

• ERROR: Add pytest pythonpath config for test discovery
• WARN: Replace deprecated locale.getdefaultlocale() with getlocale()
• WARN: Use explicit 'is not None' for XML Element check
• WARN: Move return statement out of finally block

Ran python3 -m pytest -v -W error to ensure no warnings remain.
Note: Not super confident of locale related testing since I only have English.

Checklist

• CHANGELOG.md was updated (format: - Change made (thanks to github_username))

[GB609]

Hey. Thanks for the PR and sorry for the delay.
I'm also using ArchLinux, so i would like to test and verify your changes first. I'll come back to you as soon as i can.