Assign BE and FE for verification for ~group::security policies

What does this MR do and why?

From #1518:

Since features are verified in production, most features should be verifiable by both BE and FE team members alike. Currently however the bot assigns only either BE or FE. We want to change that for groupsecurity policies

Expected impact & dry-runs

AFAICT it's not possible to dry-run this change since it doesn't use a declarative policy

---

These are strongly recommended to assist reviewers and reduce the time to merge your change.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/tree/master/doc/scheduled#testing-policies-with-a-dry-run on how to perform dry-runs for new policies.

See https://gitlab.com/gitlab-org/quality/triage-ops/-/blob/master/doc/reactive/best_practices.md#use-the-sandbox-to-test-new-processors on how to make sure a new processor can be tested.

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 #1518