Always run schema workflow on develop (#18551)

... and release branches, so that we catch any problems that slip trough
PR review.

.github/workflows/schema.yaml

@@ -5,6 +5,9 @@ on:
     paths:
       - schema/**
       - docs/usage/configuration/config_documentation.md
+  push:
+    branches: ["develop", "release-*"]
+  workflow_dispatch:
 
 jobs:
   validate-schema: