Update setup.cfg

Author: abravalheri

setup.cfg

@@ -73,7 +73,7 @@ testing =
 	# for tools/finalize.py
 	jaraco.develop >= 7.21; python_version >= "3.9" and sys_platform != "cygwin"
 	pytest-home >= 0.5
-	mypy==1.9
+	mypy==1.9  # pin mypy version so a new version doesn't suddenly cause the CI to fail
 	# No Python 3.11 dependencies require tomli, but needed for type-checking since we import it directly
 	tomli
 	# No Python 3.12 dependencies require importlib_metadata, but needed for type-checking since we import it directly