Test gap: ensure MR links are working from MR list

What does this MR do and why?

We saw in #425375 (closed) that links to MRs in the project MR list can break, this MR adds a test to ensure links are rendered.

It also adds an issue link in the title of one of the MRs, as that is what caused the issue in #425375 (closed)

How to set up and validate locally

rspec spec/features/merge_requests/user_views_all_merge_requests_spec.rb => test passes

Apply !130645 (diffs)

rspec spec/features/merge_requests/user_views_all_merge_requests_spec.rb => test fails

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.