Add a what's new entry

Hugo can choose to delete it anything

Author: johnslavik

Doc/whatsnew/3.15.rst

@@ -748,6 +748,13 @@ functools
   if it wraps a regular method and is called as a class attribute.
   (Contributed by Bartosz Sławecki in :gh:`143535`.)
 
+* When registering a callable or descriptor to :func:`functools.singledispatch`
+  or :func:`functools.singledispatchmethod` via a type annotation,
+  it is now validated that the first non-*self* or non-*cls* parameter is used.
+  Previously, a callable could be registered based on its return type
+  annotation or an irrelevant parameter type annotation.
+  (Contributed by Bartosz Sławecki in :gh:`84644`.)
+
 
 hashlib
 -------