Use hacking instead of flake8

.github/workflows/ci.yml

@@ -78,7 +78,7 @@ jobs:
         if [ "${{ matrix.os }}" != "windows-latest" ]; then
           conda install -y help2man
         fi
-        pip install flake8 pytest pytest-qt
+        pip install hacking pytest pytest-qt
 
     - name: Install main
       shell: bash -l {0}