In case Merge Requests are disabled on the project, no one should see the Merge Request button.
The project was not public and this caused a 404. So the tests were giving deceiving results. By searching for the Merge Request button in `#content-body` this is overcome, and also other Merge Request buttons (e.g. in the sidebar) are ignored.
Use shared examples to test the presence of the Merge Request button on the various pages.