Remove use of deprecated mypy option

`show_none_errors` is deprecated, see python/mypy#13507

Author: hauntsaninja

pyproject.toml

@@ -100,7 +100,6 @@ warn_no_return = true
 warn_return_any = false # TODO
 warn_unreachable = false # GH#27396
 # Suppressing errors
-show_none_errors = true
 ignore_errors = false
 enable_error_code = "ignore-without-code"
 # Miscellaneous strictness flags