bpo-43565: Document PyUnicode_KIND's return type as an unsigned int (GH-25724) (GH-27439)

(cherry picked from commit 47fd472)

Co-authored-by: Ammar Askar <[email protected]>

Author: miss-islington

Doc/c-api/unicode.rst

@@ -149,7 +149,7 @@ access internal read-only data of Unicode objects:
       ``PyUnicode_WCHAR_KIND`` is deprecated.
 
 
-.. c:function:: int PyUnicode_KIND(PyObject *o)
+.. c:function:: unsigned int PyUnicode_KIND(PyObject *o)
 
    Return one of the PyUnicode kind constants (see above) that indicate how many
    bytes per character this Unicode object uses to store its data.  *o* has to