Resolve "SAST documentation snippet is invalid"

What does this MR do?

This MR fixes an invalid example in the documentation for the SAST job.

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

I haven't tested the snippet in real condition, but linter (https://gitlab.com/ci/lint) is OK.

Why was this MR needed?

functions is undefined. This is due to a copy/paste from the auto-devops template. The example should be similar to codequality, and much more simpler.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #5040 (closed)