[3.15] Fix incorrect sentence in stable.rst (GH-149684) (GH-149814)

(cherry picked from commit 374f9d3)

Co-authored-by: Manoj K M <manojkmdev24@gmail.com>

Author: miss-islington

Doc/c-api/stable.rst

@@ -114,7 +114,7 @@ versions of Python.
 
 All functions in Stable ABI are present as functions in Python's shared
 library, not solely as macros.
-This makes them usable are usable from languages that don't use the C
+This makes them usable in languages that don't use the C
 preprocessor, including Python's :py:mod:`ctypes`.