Update build-docs.yml

added gdal install

Author: tomdurrant

.github/workflows/build-docs.yml

@@ -24,5 +24,7 @@ jobs:
                   path: ~/.cache
                   restore-keys: |
                       mkdocs-material-
+            - name: Install GDAL
+              run:  sudo apt-get update && sudo apt-get install -y gdal-bin libgdal-dev
             - run: pip install .[docs]
             - run: mkdocs gh-deploy --force