See merge request !X does not close a merge request
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### Summary
As the title states; if a commit message contains "See merge request !X" it will not close a merge request. Even though that is exactly what gilab produces - to close a merge request (successfully) one has to write "Closes !X" in the commit message.
### Steps to reproduce
1. create a merge request
2. merge it locally / without the GitLab web UI
3. copy the gitlab behaviour of writing "See merge request !X" in the commit message
4. push the merge
### What is the current *bug* behavior?
The merge request will stay open, complains about no changes to be merged (no auto merge) and has to be closed (unsuccessfully) to remove it.
### What is the expected *correct* behavior?
The merge request is closed after the push
### Output of checks
This bug happens on GitLab.com
### Possible fixes
1. Change the behaviour of the GitLab Web UI to also use "Closes !X"
1. Add a possibility of closing merge request successfully
1. Add "See merge request !X" to the phrases that close a merge request
issue