Validate event import for Github Importer

What does this MR do and why?

Describe in detail what your merge request does and why.

Add additional validation for event import for github importer.

This spec is not executed as part of normal e2e functional test suite, it has a separate project set up.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Closes #370403 (closed)