feat(ci): Trigger static quality gate only on agent changes (#45947)

### What does this PR do?

Changes the static quality gate CI job to only run when there are actual agent artifact changes, rather than running on all dev branches.

The job now uses `.on_dev_branches_with_artifact_changes` instead of `.on_dev_branches` combined with `when: on_success`.

### Motivation

The static quality gate job was running on all dev branches regardless of whether there were actual changes to agent artifacts. This change optimizes CI resources by only triggering this job when relevant changes are made.

### Describe how you validated your changes

- Reviewed the change to ensure the correct rule reference is used
- The `.on_dev_branches_with_artifact_changes` rule is an existing reference used elsewhere in the CI configuration

### Additional Notes

This is a CI optimization to reduce unnecessary job runs.

Co-authored-by: nicolas.schweitzer <nicolas.schweitzer@datadoghq.com>

Author: chouetz

.gitlab/test/functional_test/static_quality_gate.yml

@@ -3,8 +3,9 @@ static_quality_gates:
   rules:
     - !reference [.except_coverage_pipeline] # Coverage pipeline creates a special artifact that will not pass the quality gate
     - !reference [.on_main_or_release_branch]
-    - !reference [.on_dev_branches]
-    - when: on_success
+    - !reference [.on_dev_branches_with_artifact_changes]
+    - when: manual
+      allow_failure: true
   image: registry.ddbuild.io/ci/datadog-agent-buildimages/docker_x64$CI_IMAGE_DOCKER_X64_SUFFIX:$CI_IMAGE_DOCKER_X64
   tags: ["arch:amd64", "specific:true"]
   needs:
@@ -75,7 +76,7 @@ manual_gate_threshold_update:
   rules:
     - !reference [.except_coverage_pipeline] # Coverage pipeline creates a special artifact that will not pass the quality gate
     - !reference [.on_main_manual]
-    - !reference [.on_dev_branches]
+    - !reference [.on_dev_branches_with_artifact_changes]
     - when: manual
       allow_failure: true
   image: registry.ddbuild.io/ci/datadog-agent-buildimages/docker_x64$CI_IMAGE_DOCKER_X64_SUFFIX:$CI_IMAGE_DOCKER_X64