use Union syntax instead of | for python 3.9 support

also, trivial copyediting

Author: wyattscarpenter

mypy/config_parser.py

@@ -257,7 +257,7 @@ def split_commas(value: str) -> list[str]:
 ]
 _TomlDict = dict[str, _TomlValue]
 _TomlDictDict = dict[str, _TomlDict]
-_ParserHelper = _TomlDictDict | configparser.RawConfigParser
+_ParserHelper = Union[_TomlDictDict, configparser.RawConfigParser]
 
 
 def _parse_individual_file(
@@ -274,7 +274,7 @@ def _parse_individual_file(
                 toml_data: _TomlDict = tomllib.load(f)
             # Filter down to just mypy relevant toml keys
             toml_data_tool = toml_data.get("tool", {})
-            if not (isinstance(toml_data_tool, dict)) or "mypy" not in toml_data_tool:
+            if not isinstance(toml_data_tool, dict) or "mypy" not in toml_data_tool:
                 # Here we might be dealing with a toml that just doesn't talk about mypy,
                 # in which case we currently just ignore it. (Maybe we should really warn?)
                 return None