Geo: Apply selective sync to design repo updates

What does this MR do?

This fixes a bug in which all design repositories are briefly synced on update, even if they are excluded by selective sync.

Resolves #233505 (closed)

This is similar to the recent fixes for:

• project/wiki create/update events: !39488 (merged)
• container repo update events: !39663 (merged)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.