[DX] Filter on files as well with --only-suffix

[samsonasik]

@TomasVotruba here also filter files in the list of withPaths(), provided other unrelated files with different suffix in config, it cause error:

There was 1 failure:

1) Rector\Tests\FileSystem\FilesFinder\FilesFinderTest::testFilterBySuffix
Failed asserting that actual size 2 matches expected size 1.

Ref #6647 (review)

[samsonasik]

Fixed 🎉

[TomasVotruba]

Thank you 👍