fix(ci): add labeled/unlabeled to sop-checklist-gate pull_request_target types

Closes mc#817.

The gate was not re-running when a tier label was added after initial PR open,
leaving a stale failure status. Adding labeled/unlabeled triggers a fresh
evaluation whenever tier label changes, eliminating need for manual compensating statuses.

.gitea/workflows/sop-checklist-gate.yml

@@ -69,7 +69,7 @@ name: sop-checklist-gate
 
 on:
   pull_request_target:
-    types: [opened, edited, synchronize, reopened]
+    types: [opened, edited, synchronize, reopened, labeled, unlabeled]
   issue_comment:
     types: [created, edited, deleted]