Do not trigger GHA workflows on forks

GHA workflows are automatically executed on forks where they fail.
This change prevents this (only for those workflows that are
automatically triggered, e.g.: on push or schedule).

.github/workflows/deploy-docs.yml

@@ -9,7 +9,7 @@ permissions:
 jobs:
   build:
     runs-on: ubuntu-latest
-    if: github.repository_owner == 'spring-projects'
+    if: ${{ github.repository_owner == 'spring-projects' }}
     steps:
       - name: Checkout
         uses: actions/checkout@v4