feat(trigger): trigger child pipeline on stable-agent-incl-ngmsi instead of main (#20533)

Author: Pythyu

.gitlab/trigger_release.yml

@@ -20,7 +20,7 @@
     # when triggered with major version 7
     - source /root/.bashrc
     - export RELEASE_VERSION=$(inv agent.version --major-version 7 --url-safe --omnibus-format)-1
-    - inv pipeline.trigger-child-pipeline --no-follow --project-name "DataDog/agent-release-management" --git-ref "main" --variables "ACTION,AUTO_RELEASE,BUILD_PIPELINE_ID,RELEASE_PRODUCT,RELEASE_VERSION,TARGET_REPO,TARGET_REPO_BRANCH"
+    - inv pipeline.trigger-child-pipeline --no-follow --project-name "DataDog/agent-release-management" --git-ref "stable-agent-incl-ngmsi" --variables "ACTION,AUTO_RELEASE,BUILD_PIPELINE_ID,RELEASE_PRODUCT,RELEASE_VERSION,TARGET_REPO,TARGET_REPO_BRANCH"
   dependencies: []
 
 trigger_auto_staging_release: