gh-109864: Make test_gettext tests order independent

[serhiy-storchaka]

• Issue: PluralFormsTestCase tests in test_gettext are not independent #109864

[miss-islington]

Thanks @serhiy-storchaka for the PR 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[bedevere-app]

GH-110502 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-110503 is a backport of this pull request to the 3.11 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows11 Bigmem 3.x has failed when building commit 1aad4fc.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/1079/builds/2460) and take a look at the build logs.
4. Check if the failure is related to this commit (1aad4fc) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/1079/builds/2460

Failed tests:

• test_os

Failed subtests:

• test_listmounts - test.test_os.Win32ListdriveTests.test_listmounts

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "R:\buildarea\3.x.ambv-bb-win11.bigmem\build\Lib\test\test_os.py", line 2713, in test_listmounts
    self.assertSetEqual(
AssertionError: Items in the first set but not the second:
'R:\\'