github: use the git checkout action to fetch all refs

Drop the separate step for fetching gh-pages branch.

Also update the checkout action to the latest version.

.github/workflows/publish-docs.yml

@@ -12,7 +12,9 @@ jobs:
   update-gh-pages:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
 
     - name: Turnstyle
       uses: softprops/turnstyle@v1
@@ -22,9 +24,6 @@ jobs:
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
-    - name: Fetch gh-pages
-      run: git fetch --no-tags --prune --depth=1 origin refs/heads/gh-pages:refs/heads/gh-pages
-
     - name: Install build dependencies
       run: |
         pip3 install --user -r docs/requirements.txt