don't check py2vs3/py3.py when running lint test with Python 2, and vice versa

Author: boegel

.github/workflows/linting.yml

@@ -22,4 +22,10 @@ jobs:
 
     - name: Run flake8 to verify PEP8-compliance of Python code
       run: |
-        flake8 --exclude ./easybuild/tools/py2vs3/py3.py
+        # don't check py2vs3/py3.py when testing with Python 2, and vice versa
+        if [[ "${{ matrix.python-version }}" =~ "2." ]]; then
+            py_excl=py3
+        else
+            py_excl=py2
+        fi
+        flake8 --exclude ./easybuild/tools/py2vs3/${py_excl}.py