cis: install pytest when running type checks

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Install tools
         run: |
           python -m pip install --upgrade pip
-          pip install flake8 black isort mypy
+          pip install flake8 black isort mypy pytest
           pip install git+https://github.com/pyvisa/pyvisa.git#egg=pyvisa
       - name: Isort
         run: |