adds step to install gdal

Author: chalmerlowe

.github/workflows/unittest.yml

@@ -21,6 +21,8 @@ jobs:
       run: |
         python -m pip install --upgrade setuptools pip wheel
         python -m pip install nox
+    - name: Install GDAL
+      run: sudo apt-get update && sudo apt-get install -y libgdal-dev
     - name: Run unit tests
       env:
         COVERAGE_FILE: .coverage-${{ matrix.python }}