Use PEP 604 syntax wherever possible (#7493)

stubs/PyMySQL/pymysql/converters.pyi

@@ -2,9 +2,9 @@ import datetime
 import time
 from collections.abc import Callable, Mapping, Sequence
 from decimal import Decimal
-from typing import Any, Optional, TypeVar
+from typing import Any, TypeVar
 
-_EscaperMapping = Optional[Mapping[type[object], Callable[..., str]]]
+_EscaperMapping = Mapping[type[object], Callable[..., str]] | None
 _T = TypeVar("_T")
 
 def escape_item(val: object, charset: object, mapping: _EscaperMapping = ...) -> str: ...