fix fail test run with enabled junit.testFilter option

[Sparkymann]

Hi! There is a problem if you enable the junit.testFilter setting, and there are other tests in the project besides arch-unit
Exception:

Caused by: org.junit.platform.commons.PreconditionViolationException: cannot remove the root of a hierarchy

In PR fix a condition so that non-ArchUnit descriptors are not checked
Tested the changes in my test repository https://github.com/Sparkymann/archunit-test
Failed workflow: https://github.com/Sparkymann/archunit-test/pull/1/checks
Corrected: https://github.com/Sparkymann/archunit-test/pull/3/checks

[codecholeric]

Thanks a lot for taking care of this! I do have one suggestion that I added as a fixup (see the commit message for the reasoning). In a nutshell, I think we can solve it a little safer by checking isRoot() instead of relying on the ArchUnit internal class hierarchy.
Does this make sense to you? Then I'd squash and merge it...

[codecholeric]

BTW: To get throught the CI commits also need a DCO sign-off in your commit message (see https://github.com/TNG/ArchUnit/blob/main/DCO#L34). If you're fine with that I could also add the line for you if you want 😉

[Sparkymann]

Hi! I'm sorry for the long wait.

I do have one suggestion

Thank you, I agree with your suggestion, it looks like more general decision

If you're fine with that I could also add the line for you if you want

I would be very grateful to you.