Ensure doc dependencies are installed when deploying

.github/workflows/docs.yml

@@ -40,7 +40,6 @@ jobs:
 
       - name: Build docs
         run: mkdocs build
-
       - name: Upload static docs
         uses: actions/upload-artifact@v3
         with:
@@ -53,5 +52,27 @@ jobs:
     if: "startsWith(github.ref, 'refs/tags/')"
     needs: [build]
     steps:
+      - name: Checkout source
+        uses: actions/checkout@v3
+
+      - name: Install python
+        uses: actions/setup-python@v4
+        with:
+          python-version: 3.x
+
+      - run: echo "cache_id=$(date --utc '+%V')" >> $GITHUB_ENV
+
+      - uses: actions/cache@v3
+        with:
+          key: mkdocs-material-${{ env.cache_id }}
+          path: .cache
+          restore-keys: |
+            mkdocs-material-
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install ".[doc]"
+
       - name: Deploy to github pages
         run: mkdocs gh-deploy --force