[EE] Resolve two QA failures

What does this MR do?

This solves two issues in our QA scenarios:

1. When trying to expand a settings section, it seems we were looking at the whole section content to match, but that could returns several elements. We now restrict the match to the sections' headers.

2. When asserting that a MR has been created, depending on how fast the instance is, the message could be Opened x seconds ago instead of Opened less than a minute ago or Opened about a minute ago. This losen the match.

Note: We might need a specific MR for the 11-0-stable branch since the section header was changed from Merge request settings (in 11-0-stable) to Merge request (in master).

Are there points in the code the reviewer needs to double check?

If all the scenarios still pass, then I think we're good.

Does this MR meet the acceptance criteria?

• Conform by the code review guidelines
  • Has been reviewed by a Backend maintainer
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Fixes gitlab-qa#271 (closed).