Do not nudge for auto-merge in security project

Context

From !3042 (comment 2131718989):

I wonder if we need to exclude security merge requests from this processor. Security merge requests are only merged during the patch release window. From the Slack announcement:

gitlab-bot will nudge the latest approver when an MR wasn’t set to auto-merge AND the MR could be merged, or when the MR is set to auto-merge, but cannot be merged (e.g. when an unresolved discussion was added).

I suspect the bot will nudge the latest approver on a security merge request encouraging them to merge, but they won't be able to; aside from only merging on patch release window, security merge requests can only be merged by the gitlab-release-tools-bot.

What does this MR do and why?

Do not nudge for auto-merge in the security project.

Expected impact & dry-runs

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