Increase test coverage of `gettext`

[tomasr8]

The test coverage for these functions is low as there are no dedicated tests for them. I propose we add tests for these functions.
This will come in handy if/when we decide to fix #64243.

Linked PRs

• gh-130655: Increase test coverage of gettext._expand_lang #130656
• [3.13] gh-130655: Increase test coverage of gettext._expand_lang() (GH-130656) #130671
• [3.12] gh-130655: Increase test coverage of gettext._expand_lang() (GH-130656) #130672
• gh-130655: Add tests for gettext.find() #130691
• gh-130655: Add a test for bad magic numbers when parsing gettext MO files #131909
• gh-130655: Add a test for corrupt MO files in gettext #131911
• [3.13] gh-130655: Add a test for bad magic numbers in .mo files parsed by gettext (GH-131909) #132077
• [3.12] gh-130655: Add a test for bad magic numbers in .mo files parsed by gettext (GH-131909) #132078
• [3.13] gh-130655: Add a test for corrupt .mo files in gettext (GH-131911) #132079
• [3.12] gh-130655: Add a test for corrupt .mo files in gettext (GH-131911) #132080
• [3.12] gh-130655: Add tests for gettext.find() (GH-130691) #132083
• [3.13] gh-130655: Add tests for gettext.find() (GH-130691) #132084
• gh-130655: Move test_gettext data to a separate file  #132442
• gh-130655: Add a test for big-endian MO files in gettext #132469
• [3.13] gh-130655: Add a test for big-endian MO files in gettext (GH-132469) #133248
• gh-130655: add tests for dgettext #134594

[StanFromIreland]

I'll open a PR for find sometime tomorrow :-)