Change the only keyword to use the newer rules syntax

docs/publishing-your-site.md

@@ -122,15 +122,14 @@ contents:
     image: python:latest
     pages:
       stage: deploy
-      only:
-        - master # (1)!
-        - main
       script:
         - pip install mkdocs-material
         - mkdocs build --site-dir public
       artifacts:
         paths:
           - public
+      rules:
+        - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'
     ```
 
     1.  At some point, GitLab renamed `master` to `main`. If your default branch
@@ -142,15 +141,14 @@ contents:
     image: python:latest
     pages:
       stage: deploy
-      only:
-        - master
-        - main
       script: # (1)!
         - pip install git+https://${GH_TOKEN}@github.com/squidfunk/mkdocs-material-insiders.git
         - mkdocs build --site-dir public
       artifacts:
         paths:
           - public
+      rules:
+        - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH'
     ```
 
     1.  Remember to set the `GH_TOKEN` environment variable to the value of your