flake8/pre-commit: ignore invalid "whitespace before ':'"

E203 error occurs due to black formatting - see psf/black#280

https://github.com/psf/black/blob/main/docs/compatible_configs/flake8/setup.cfg

Author: e3krisztian

Diff for: setup.cfg

@@ -1,6 +1,9 @@
 [flake8]
 # We start with a strict setting, this is ranked as A in radon
 max-complexity = 8
-ignore = E501,W503
+ignore =
+    E501  # line too long
+    W503  # line break before binary operator
+    E203  # whitespace before ':' - known black/flake8 incompatibility
 exclude =
     __init__.py