Users who don't have permission to create merge request can see merge request button (and creating leads to 404) in "Compare" view
Summary
Users who don't have permission to create a merge request should not be able to see merge request button or button should be grayed out and un-clickable. The permission error is a valid one, but it tends to confuse people why the button is available in the first place.
Steps to reproduce
On reporter or guest permissions on an updated branch, navigate to 'Compare' tab under repository.
Expected behavior
You shouldn't be able to see the button or at least click it.
Actual behavior
The button leads to a 404
Relevant logs and/or screenshots
