ci: set runner group on parallel jobs (#6916)

.github/workflows/core-integration-test.yml

@@ -16,6 +16,10 @@ on:
 jobs:
   postgres:
     runs-on: ubuntu-latest
+    # TODO: use runner group as soon as integration tests run in parallel
+    # Currently it only consumes time and adds no value
+    # runs-on:
+    #   group: zitadel-public
     services:
       postgres:
         image: postgres