Fix typos about .gitlab-ci.yml in Serverless docs

What does this MR do?

Fixes typos about .gitlab-ci.yml in Serverless docs.

What are the relevant issue numbers?

#55621 (closed)

Does this MR meet the acceptance criteria?

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