DEV: modifies CI to execute flake8 on PR updates

.github/workflows/linters.yml

@@ -28,14 +28,16 @@ jobs:
         python -m pip install --upgrade pip
         pip install .[all]
         pip install .[tests]
-        pip install pylint isort
+        pip install pylint isort flake8 black
     - name: Run isort
       run: isort --check-only rocketpy/ tests/ docs/ --profile black
     - name: Run black
       uses: psf/black@stable
       with:
         options: "--check rocketpy/ tests/ docs/"
         jupyter: true
+    - name: Run flake8
+      run: flake8 rocketpy/ tests/
     - name: Run pylint
       run: |
         pylint rocketpy/