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

stdlib/rlcompleter.pyi

@@ -1,5 +1,5 @@
-from typing import Any, Dict, Optional
+from typing import Any, Dict
 
 class Completer:
-    def __init__(self, namespace: Optional[Dict[str, Any]] = ...) -> None: ...
-    def complete(self, text: str, state: int) -> Optional[str]: ...
+    def __init__(self, namespace: Dict[str, Any] | None = ...) -> None: ...
+    def complete(self, text: str, state: int) -> str | None: ...