run on ubuntu-2004-xl in openapi dev mode check (github#28580)

* run on ubuntu-20.04-xl in 'OpenAPI dev mode check'

* self-check also

Author: peterbe

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

@@ -24,6 +24,7 @@ on:
       - 'script/rest/**/*.json'
       - 'package*.json'
       - 'lib/redirects/static/**/*.json'
+      - '.github/workflows/openapi-schema-check.yml'
 
 permissions:
   contents: read
@@ -36,7 +37,7 @@ concurrency:
 jobs:
   check-schema-versions:
     if: ${{ github.repository == 'github/docs-internal' }}
-    runs-on: ${{ fromJSON('["ubuntu-latest", "self-hosted"]')[github.repository == 'github/docs-internal'] }}
+    runs-on: ubuntu-20.04-xl
     steps:
       - name: Checkout repository code
         uses: actions/checkout@dcd71f646680f2efd8db4afa5ad64fdcba30e748