Only run the OpenAPI schema check workflow for the internal repo (#17788)

Author: JamesMGreene

.github/workflows/openapi-schema-check.yml

@@ -3,9 +3,13 @@ name: OpenAPI dev mode check
 on:
   workflow_dispatch:
   push:
+    branches:
+      - main
+  pull_request:
 
 jobs:
   check-schema-versions:
+    if: ${{ github.repository === 'github/docs-internal' }}
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository code