[QA] Add a log-out step and expectation to `qa/qa/specs/features/browser_ui/1_manage/login/log_in_spec.rb`

What does this MR do?

Reopening of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21862.

This adds a log-out step and expectation to qa/qa/specs/features/browser_ui/1_manage/login/log_in_spec.rb.

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/52700.

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer