Add not labels filters to stuck bugs heatmap

What does this MR do and why?

Add not labels filters to stuck bugs heatmap

This fixes no severity links.

Expected impact & dry-runs

Didn't make dry-runs but I think tests should make it clear this should be fixed?

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (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 #1449 (closed)