Run differential ShellCheck on merge_group

.github/workflows/differential-shellcheck.yml

@@ -5,6 +5,9 @@ on:
   push:
   pull_request:
     branches: [ main ]
+  merge_group:
+    branches:
+      - main
 
 permissions:
   contents: read
@@ -43,6 +46,9 @@ jobs:
             src/**.{zsh,osh}
           display-engine: sarif-fmt
           token: ${{ secrets.GITHUB_TOKEN }}
+          triggering-event: ${{ github.event_name == 'merge_group' && 'manual' || github.event_name }}
+          base: ${{ github.event.merge_group.base_sha }}
+          head: ${{ github.event.merge_group.head_sha }}
 
       - if: always()
         name: Upload artifact with defects in SARIF format