Some tests are skipped in `test_gettext`

[tomasr8]

Bug report

Bug description:

PluralFormsInternalTestCase does not inherit from unittest.TestCase so the test is not picked up:

cpython/Lib/test/test_gettext.py

Lines 405 to 407 in 9837c2a

	class PluralFormsInternalTestCase:
	# Examples from http://www.gnu.org/software/gettext/manual/gettext.html

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-130177: Fix skipped tests in test_gettext #130178
• [3.13] gh-130177: Fix unintentionally skipped tests in test_gettext (GH-130178) #130183
• [3.12] gh-130177: Fix unintentionally skipped tests in test_gettext (GH-130178) #130184

[serhiy-storchaka]

Thanks @tomasr8 for noticing and fixing this.