ci: update check-approver to trigger on pull request review submission

Instead of triggering on pull request events, we'll now trigger on
review submissions. This will handle the case where an approval was not
immediately triggering the workflow.

.github/workflows/check-approver.yaml

@@ -1,8 +1,8 @@
 name: Check Approver
 
 on:
-  pull_request:
-    types: [opened, edited, synchronize]
+  pull_request_review:
+    types: [submitted]
 
 permissions: read-all