Added install of pytest to linting step to satisfy mypy

Author: RobertoRoos

.github/workflows/lint.yml

@@ -29,7 +29,8 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        python -m pip install .[lint]
+        python -m pip install .[lint] pytest
+      # Also install pytest here, otherwise mypy will complain about our test files
 
     - name: Lint with Ruff
       run: ruff check . --output-format github