Convert FileTransferTest into a Kernel test

Very weird test IMHO.

Maybe needs full refactoring?
For me, that would be for a follow-up issue.

Unsure if we should just do the full refactor here or not. In the meantime, one comment on a test method.

I think refactoring the test only might not be enough, all the "magic" that happens around here https://git.drupalcode.org/project/drupal/-/blob/11.x/core/lib/Drupal/Co... makes me a bit cringy...

Also stuff seems to be broken already: 🐛 [regression] FTPExtension class can no longer connect as of 9.5.x Needs work

So at this point in time I'm unsure what to do.

For now I addressed the thread in the MR created by @longwave, but as mentioned in the comment, that also increases my cringe-level.

Coverage doesn't appear lost but this one I'd probably wait for a 2nd +1 RTBC before marking.

Per https://www.drupal.org/project/drupal/releases/10.2.0 →
Drupal core automated tests and test APIs are being converted to require strict typing in all cases. So far, Drupal core test traits, build tests, and functional JavaScript tests all require strict typing. Going forward, all Drupal core tests will require strict typing. It is recommended that contributed and custom projects use the Drupal standard for strict type declaration.

Added strict type and fixed phpcs issues.

Actually this is converting an existing test. Adding strict typing seems out of scope for this issue

Thank smustgrave for providing clarification on the scope. I've removed the strict type declaration and made some adjustments to adhere to coding standards.

We should go back to commit https://git.drupalcode.org/project/drupal/-/merge_requests/6443/diffs?co... rest appears to be out of scope of the issue.