fix: linter check for black and isort not failing when changes requir…

…ed (#631)

- black and isort returncode is 0 when fixes required and applied, so
  add arguments that make it returncode 1 when fixes required
- flake8 and pycodestyle return 1 already

.github/workflows/verify.yml

@@ -30,8 +30,8 @@ jobs:
           pip list
 
       # Linters.
-      - run: black pyxform tests
-      - run: isort pyxform tests
+      - run: black pyxform tests --check --diff
+      - run: isort pyxform tests --check-only --diff
       - run: flake8 pyxform tests
       - run: pycodestyle pyxform tests
 

pyxform/xlsparseutils.py

@@ -1,7 +1,7 @@
 import re
-from pyxform import constants
 from typing import KeysView, Optional
 
+from pyxform import constants
 from pyxform.utils import levenshtein_distance
 
 # http://www.w3.org/TR/REC-xml/