Update tests.yml

Author: AttackingOrDefending

.github/workflows/tests.yml

@@ -28,6 +28,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install flake8 pytest
+        pip install numpy
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names