Ignore `locale/gitlab.pot` in ee_compat_check

What does this MR do?

This makes the ee_compat_check ignore conflicts in locale/gitlab.pot, the conflicts can be resolved in the CE -> EE merge by running bundle exec rake gettext:find; git checkout locale/*/gitlab.po.

There is a discussion about automating this away in https://gitlab.com/gitlab-org/release-tools/issues/183#note_61707476, but for now I think this would avoid having to create an EE-mr, regenerating the file in EE, merge both CE & EE, and then resolve the conflict on the timestamp.

/cc @leipert