Resolve "JiHu AppSec Notifier wasn't triggered on a JiHu Contribution"

What does this MR do and why?

Fix missing pinging AppSec when thread is already there

• We use a new unique comment for PingAppSecOnApproval
• We check against this new unique comment
• However we still try to attach to the old thread

Expected impact & dry-runs

NOTE: The existing merge requests can be pinged again because we used a new unique comment for the ping.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review

Closes #1058 (closed)