Updates use of sha for linting

What does this MR do?

Feature flag must be turned on: pipeline_editor_empty_state_action

Pipeline editor flow to replicate:

1. Create new, empty project
2. Go to "Pipeline Editor" section
3. Click on Create new CI/CD Pipeline

This will bring you to the pipeline editor. You can type anything and there shouldn't be any errors, outside of linting validations.

Note: This MR only fixes the error undefined method sha for nil, it does not add functionality.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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  • I have included a changelog entry.
  • I have not included a changelog entry because it doesn't need one.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

#323223 (closed)