E2E: Update imported mr validation for github import spec

What does this MR do and why?

Update validations for imported mr from github to account for added assignee and reviewer

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 #377410 (closed), #386716 (closed)