Prevent blocked user from triggering notifications for comments

What does this MR do?

Prevent blocked user from triggering notifications for comments. This is useful as potentially there might be instances where SIRT can't delete the user but we still want to prevent mass-emails from being sent. See !53699 (merged) for similar but with a Ghost User (deleted user)

Related issue: https://gitlab.com/gitlab-org/gitlab/-/issues/320994

Screenshots (strongly suggested)

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.