docs: Install both package and dev dependencies before generating docs

.github/workflows/docs.yaml

@@ -13,6 +13,7 @@ jobs:
       - uses: actions/setup-python@v4
       - name: Install dependencies
         run: |
+          pip install -r requirements.txt
           pip install -r requirements_dev.txt
       - name: Sphinx build
         working-directory: ${{ github.workspace }}/docs