Accept `AsyncIterable` for responses

CHANGES.rst

@@ -4,6 +4,9 @@ Version 3.1.1
 Unreleased
 
 -   Fix type hint for `cli_runner.invoke`. :issue:`5645`
+-   Mark sans-io base class as being able to handle views that return
+    ``AsyncIterable``. This is not accurate for Flask, but makes the type
+    accurate for Quart. :pr:`5659`
 
 
 Version 3.1.0

src/flask/typing.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import collections.abc as cabc
 import typing as t
 
 if t.TYPE_CHECKING:  # pragma: no cover
@@ -17,6 +18,8 @@ ResponseValue = t.Union[
     t.Mapping[str, t.Any],
     t.Iterator[str],
     t.Iterator[bytes],
+    cabc.AsyncIterable[str],
+    cabc.AsyncIterable[bytes],
 ]
 
 # the possible types for an individual HTTP header