Only deploy docs when docs have changed

.github/workflows/ci.yml

@@ -45,7 +45,14 @@ jobs:
     if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/master' }}
     steps:
       - uses: actions/checkout@v3
+      - name: Get changed files
+        id: changed-files
+        uses: tj-actions/changed-files@v34
+        with:
+          files: |
+            docs/**
       - name: Deploy docs
+        if: steps.changed-files.outputs.any_changed == 'true'
         uses: mhausenblas/mkdocs-deploy-gh-pages@master
         env:
           GITHUB_TOKEN: ${{ secrets.github_token }}