We should enable ee_compat_check for community branches too

Apparently https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/12968 requires an EE version as well, and figuring this out during the merge from CE to EE could be frustrating. Here's an attempt to fix it: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2886 but this is in a rush and might not fix it properly.

What's the downside of enabling this for all the branches?