fix: remove synchronize trigger from review gate

When renovate pushes new commits, the synchronize event re-runs the
review gate and creates a failing pull_request run that overwrites the
passing pull_request_review run.

Author: peter-svensson

.github/workflows/review-gate.yaml

@@ -2,7 +2,7 @@ name: Review Gate
 
 on:
   pull_request:
-    types: [opened, synchronize, reopened]
+    types: [opened, reopened]
   pull_request_review:
     types: [submitted]