hack around python/mypy#17566

Author: asottile

add_trailing_comma/_data.py

@@ -23,7 +23,8 @@ class State(NamedTuple):
 TokenFunc = Callable[[int, list[Token]], None]
 ASTFunc = Callable[[State, AST_T], Iterable[tuple[Offset, TokenFunc]]]
 
-FUNCS = collections.defaultdict(list)
+FUNCS: ASTCallbackMapping  # python/mypy#17566
+FUNCS = collections.defaultdict(list)  # type: ignore[assignment]
 
 
 def register(tp: type[AST_T]) -> Callable[[ASTFunc[AST_T]], ASTFunc[AST_T]]: