Consider refactoring the secure MR tests to reduce the overall test duration

The following discussion from !20479 (merged) should be addressed:

• @mlapierre started a discussion: (+4 comments)

  All together this test is now quite slow:

  62.75 seconds average (251 seconds / 4 examples) ./qa/specs/features/ee/browser_ui/secure/create_merge_request_with_secure_spec.rb:6

  I'm not too familiar with the feature, but it looks like at least some of the tests could re-use the same setup. Would it be possible to change this to before(:context)? Or at least share some of the setup between tests (e.g., even if a new MR is needed for each test, it looks like everything up to the MR could be shared).

See the discussion for more details. Essentially, reducing the test duration won't be as simple as sharing the project between all the tests.