Install pytest-cov in the testing workflow

Author: AA-Turner

.github/workflows/ci.yml

@@ -46,7 +46,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          python -m pip install .[test]
+          python -m pip install .[test] pytest-cov
       - name: Test with pytest
         run: >
           python -m pytest