Ruby Coverage: Adjust group filters to avoid greedy files matches

The following discussion from !124957 (merged) should be addressed:

• @splattael started a discussion:

  Question According to https://gitlab-org.gitlab.io/-/gitlab/-/jobs/4564435390/artifacts/coverage/index.html#_Config this is also matching non-config related files like ee/lib/gitlab/auth/oidc/config.rb because it uses String#include? to filter files.

  Is this intended? 🤔

  

  If we want to match files starting with config or ee/config should we use RegexpFilter instead?

  Suggestion (untested)

        add_group 'Config',       %r{^/(ee/)?config}

  I guess same goes for other group definitions as well. For example, Tooling:

  https://gitlab-org.gitlab.io/-/gitlab/-/jobs/4564435390/artifacts/coverage/index.html#_Tooling

  Having said that let's fix it in a follow-up. 💪