util: use types from wsgiref.types

These were only added in 3.11, but it's fine if type checking only
works in more recent versions

src/fava/util/__init__.py

@@ -22,9 +22,9 @@
     from typing import Callable
     from typing import ParamSpec
     from typing import TypeVar
+    from wsgiref.types import StartResponse
+    from wsgiref.types import WSGIEnvironment
 
-    from _typeshed.wsgi import StartResponse
-    from _typeshed.wsgi import WSGIEnvironment
     from babel import Locale
     from flask.wrappers import Response