FEAT Phpunit - update i18n suite for windows / phpunit 10 compatibility

[lekoala]

Description

I tried to run the test suite without warnings on my local machine. Phpunit 9 complains about Phpunit 10 deprecation. I found a nice way around that could be migrated to SapphireTest for other test suites.

I've also made some changes to be able to run this on windows. This should not affect linux/mac os.

Manual testing steps

Run the 18n test suite
See that you get no phpunit 10 deprecation
See that all works well on windows

Issues

#11525 (i'm creating the test for this, and it's easier to work with a test suite that is not making warnings :) )

Pull request checklist

• The target branch is correct
  • See picking the right version
• All commits are relevant to the purpose of the PR (e.g. no debug statements, unrelated refactoring, or arbitrary linting)
  • Small amounts of additional linting are usually okay, but if it makes it hard to concentrate on the relevant changes, ask for the unrelated changes to be reverted, and submitted as a separate PR.
• The commit messages follow our commit message guidelines
• The PR follows our contribution guidelines
• Code changes follow our coding conventions
• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green

[GuySartorelli]

The linked issue doesn't seem related.

[lekoala]

@GuySartorelli i know, i can create one or two separate issues if needed

basically the issue are:

• test suite doesn't work on windows (which may be a non goal, but here in my case, fixing it has no downside so why not)
• test suite triggers phpunit 10 deprecation warning (which will be an issue at some point, and it makes working with the test suite more annoying than necessary)