FIX: Typing of FuncAnimation

`func` and `init_func` may return None (which is ok if `blit=False`).
Since gating the allowed signature on the state of `blit` is not
feasible, we err on the side on being too permissive in the type
definition: Rather not flag a type error and only raise on runtime than
complain on an actually working signature.

Author: timhoffm

lib/matplotlib/animation.pyi

@@ -206,9 +206,9 @@ class FuncAnimation(TimedAnimation):
     def __init__(
         self,
         fig: Figure,
-        func: Callable[..., Iterable[Artist]],
+        func: Callable[..., Iterable[Artist] | None],
         frames: Iterable | int | Callable[[], Generator] | None = ...,
-        init_func: Callable[[], Iterable[Artist]] | None = ...,
+        init_func: Callable[[], Iterable[Artist] | None] | None = ...,
         fargs: tuple[Any, ...] | None = ...,
         save_count: int | None = ...,
         *,