Fix docs typo in Validate the .gitlab-ci.yml

What does this MR do?

Fixes a typo in docs introduced in !17729 (merged).

Does this MR meet the acceptance criteria?

• [n/a] Changelog entry added, if necessary
• Documentation created/updated
• [n/a] API support added
• [n/a] Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • [n/a] Has been reviewed by Backend
  • [n/a] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [n/a] Internationalization required/considered
• [n/a] End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #45688 (closed)