Fix list-translations() ordering in tests

[k0tran]

So the list_translations() method uses os.listdir() without any additional params. This can yield different results on different machines:

# ...
                if any(x.endswith(".mo") for x in os.listdir(locale_dir)):
                    result.append(Locale.parse(folder))
# ...

For example:

$ python3 -python3 -c "print(__import__('os').listdir('./tests/translations'))"
['messages.pot', 'ja', 'de', 'fr'] # on my x64_64 machine
['fr', 'messages.pot', 'de', 'ja'] # on my loongarch64 machine

The documentation of list_translations() say nothing about translations ordering. So I've decided that it's error in tests hence this PR is changing them rather that list_translations() method.