The `ee_compat_check` job should fail if an EE MR isn't merged for the EE-branch

The trick is as follows:

sha = `git rev-parse origin/<ee-branch>`
`git ls-remote -q origin merge-requests\*\head | grep #{sha} | sed 's/.*refs\/merge-requests\/\([0-9]*\)\/head/\1/g'`

Also, we could even make it fail if the EE MR is not green.

The rationale for this is that as we'll perform upstream merges every few hours, it's very important that a CE change that needs EE-specific changes isn't merged before its EE counterpart.

If that's not the case, someone will need to solve the conflict and potentially figure out the parts that need to be changed in EE in the CE->EE upstream MR, but that would be a shame since this work would have already been done in a specific EE MR, which isn't merged yet.