[3.9] bpo-46609: Update asyncio-task coroutine doc (GH-31132)

@coroutine in removed in 3.11, not 3.10.
(cherry picked from commit 5603db4)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Author: miss-islington

Doc/library/asyncio-task.rst

@@ -991,7 +991,7 @@ Generator-based Coroutines
 .. note::
 
    Support for generator-based coroutines is **deprecated** and
-   is scheduled for removal in Python 3.10.
+   is removed in Python 3.11.
 
 Generator-based coroutines predate async/await syntax.  They are
 Python generators that use ``yield from`` expressions to await
@@ -1019,7 +1019,7 @@ enforced.
     This decorator should not be used for :keyword:`async def`
     coroutines.
 
-    .. deprecated-removed:: 3.8 3.10
+    .. deprecated-removed:: 3.8 3.11
 
        Use :keyword:`async def` instead.