fix: add merge_group trigger to unblock merge queue

[olegsu]

Summary

• Added merge_group: trigger to 4 workflow files so CI runs during GitHub merge queue processing
• Fixed stale .mergify.yml queue_rules that referenced a previous CI system's check names

Root Cause

GitHub's native merge queue fires a merge_group event for each batch of queued PRs. Without this trigger in the workflow files, no checks ran on merge queue commits. The required status checks (Lint, Unit Test, Package Cloudbeat, Manifest Tests, Test Rego Policies) were never reported, leaving the queue stuck in AWAITING_CHECKS indefinitely.

Fixes

Workflows (added merge_group: trigger)

File	Checks produced
ci-pull_request.yml	Lint, Unit Test
packaging.yml	Package Cloudbeat (docker), Package Cloudbeat (tar.gz)
unit-test.yml	Manifest Tests
test-opa-policies.yml	Test Rego Policies

.mergify.yml queue_rules

Replaced 6 non-existent check names (from old Cloudbeat-CI system) with the correct current check names.

Test plan

• Verify CI triggers on this PR normally (pull_request event)
• Once merged, verify the merge queue triggers CI via merge_group event
• Confirm stuck Renovate PRs (chore(deps): update module github.com/klauspost/compress to v1.18.5 (main) #4335, chore(deps): update module github.com/fxamacker/cbor/v2 to v2.9.1 (main) #4328, chore(deps): update module github.com/go-ldap/ldap/v3 to v3.4.13 (main) #4332, chore(deps): update module github.com/go-chi/chi/v5 to v5.2.5 (main) #4329, chore(deps): update module github.com/google/certificate-transparency-go to v1.3.3 (main) #4334) process correctly

🤖 Generated with Claude Code

[mergify]

This pull request does not have a backport label. Could you fix it @olegsu? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.