Updating a closed/merge Gitlab merge requests creates new environments

[rocketeerbkw]

Describe the bug

I noticed some ancient PR environments on a Gitlab based repo and assumed they hadn't been cleaned up properly, but the created date was recent.

Looking at the merge request history, the event that corresponds to the creation date was "User A unassigned User B 2 months ago." This happened for two merge requests, one was closed and one was merged.

Seems like the webhook handler got confused and thought these were new/created merge requests?

To Reproduce

I assume this will work, but untested:

1. Open a merge request, see that PR environment is created
2. Assign a user to the merge request
3. Close the merge request, see that the PR environment is deleted
4. Unassign the user
5. See that PR environment is created again

Expected behavior

PR environments shouldn't exist for closed/merged merge requests.