docs: upgrade pip before building docs

.github/workflows/docs.yml

@@ -12,7 +12,9 @@ jobs:
     steps:
       - name: Checkout main
         uses: actions/checkout@v2
-
+      - name: Upgrade pip
+        run: |
+          python -m pip install --upgrade pip
       - name: Deploy docs
         uses: mhausenblas/mkdocs-deploy-gh-pages@master
         # Or use mhausenblas/mkdocs-deploy-gh-pages@nomaterial to build without the mkdocs-material theme