Resolve "Admin/Overview/Users mobile view"

What does this MR do?

Fixes mobile layout issues on /admin/users page.

• Fixes control element placement when long usernames or email addresses overflow their container
• Fixes condensed dropdown menu (issue caused by acde2e30)

Before:

After:

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

Ensure css changes don't have any side effects elsewhere in GitLab. (I don't think they would...)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #22746 (closed)