Big diff: Use new "|" union syntax (#5872)

stdlib/_csv.pyi

@@ -1,4 +1,4 @@
-from typing import Any, Iterable, Iterator, List, Optional, Protocol, Type, Union
+from typing import Any, Iterable, Iterator, List, Protocol, Type, Union
 
 QUOTE_ALL: int
 QUOTE_MINIMAL: int
@@ -9,8 +9,8 @@ class Error(Exception): ...
 
 class Dialect:
     delimiter: str
-    quotechar: Optional[str]
-    escapechar: Optional[str]
+    quotechar: str | None
+    escapechar: str | None
     doublequote: bool
     skipinitialspace: bool
     lineterminator: str