New attribute `#[RequiresPhpUnitExtension(SomeExtension::class)]`

[nikophil]

When developing a library which provides a PhpUnit extension, it would be useful to be able to skip some tests which do require this extension.

WDYT of a new attribute which would skip tests if the given extension is not enabled?

Maybe it can be nice to allow this attribute to be repeatable, or to accept multiple parameters, for the rare cases where two extensions are required for the given test?