Ensure wiki cache expires correctly in PostReceive

What does this MR do?

This fixes an issue where wiki cache is causing Elastic indexing to not happen after creating a new page.

All this MR changes is that we use the same cache invalidation logic for project repo push now in wiki repo push. It seemed to be missing from the wiki repo push handling.

You can reproduce this bug by simply creating a new project, adding a wiki page and then trying to search for it. It doesn't get indexed because it thinks the wiki is empty due to the stale cache.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team