ci: isort: use CLI interface instead of official isort/isort-action…

… which appears to have bugs and config documentation gaps

.github/workflows/python-package.yml

@@ -32,10 +32,12 @@ jobs:
     - name: Install project
       run: poetry install
     - name: Lint imports with isort
-      # By default: exit with error if imports are not properly sorted
-      uses: isort/isort-action@master
-      with:
-        configuration: profile = black
+      # Use command line due to bugs/doc gaps with official `isort/isort-action`.
+      # Exit with error if the code is not properly formatted; show diffs;
+      # `black` compatibility
+      run: |
+        source $VENV
+        isort . --check-only --diff --profile black
     - name: Lint with black
       # by default: exit with error if the code is not properly formatted; show diffs
       uses: psf/black@stable