Add merge group event to image-builder-test (#12385)

.github/workflows/pull-image-builder-test.yml

@@ -8,6 +8,7 @@ on:
       - ".github/workflows/image-builder.yml"
       - ".github/actions/expose-jwt-action/**"
       - ".github/actions/image-builder/**"
+  merge_group:
 
 permissions:
   id-token: write # This is required for requesting the JWT token
@@ -40,4 +41,4 @@ jobs:
     needs: build-image
     steps:
       - name: Test image
-        run: echo "Testing images ${{ needs.build-image.outputs.images }}"
+        run: echo "Testing images ${{ needs.build-image.outputs.images }}"