Add requirements.txt install step

.github/workflows/pylint.yml

@@ -14,10 +14,13 @@ jobs:
       uses: actions/setup-python@v3
       with:
         python-version: ${{ matrix.python-version }}
+    - name: Set up Python path
+      run: echo "PYTHONPATH=$PWD" >> $GITHUB_ENV
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install pylint
+        pip install flake8 pytest
+        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     - name: Analysing the code with pylint
       run: |
         pylint $(git ls-files '*.py')