MarkupInterfaceComparator function signatures not compatible with PHPUnit 10

Quick patch to confirm the return types don't cause problems in PHPUnit 9.

Seems like a simple enough change, don't think it should cause any BC issue.

I'm triaging RTBC issues → . I read the IS and the comments and the MR. I didn't find any unanswered questions or other work to do.

I updated credit

Leaving at RTBC.

As this is a return type change and we aren't ready for PHPUnit 10 otherwise, committing this to 11.x (10.3.x) only.

Committed b0de5c1 and pushed to 11.x. Thanks!

Automatically closed - issue fixed for 2 weeks with no activity.