Fix PyUnicode_Fill() doc: return type is Py_ssize_t, not int

Doc/c-api/unicode.rst

@@ -564,7 +564,7 @@ APIs:
    .. versionadded:: 3.3
 
 
-.. c:function:: int PyUnicode_Fill(PyObject *unicode, Py_ssize_t start, \
+.. c:function:: Py_ssize_t PyUnicode_Fill(PyObject *unicode, Py_ssize_t start, \
                         Py_ssize_t length, Py_UCS4 fill_char)
 
    Fill a string with a character: write *fill_char* into

Doc/whatsnew/3.3.rst

@@ -828,7 +828,7 @@ Functions and macros manipulating Py_UNICODE* strings:
  * :c:macro:`Py_UNICODE_strncmp`: use :c:func:`PyUnicode_Tailmatch`
  * :c:macro:`Py_UNICODE_strchr`, :c:macro:`Py_UNICODE_strrchr`: use
    :c:func:`PyUnicode_FindChar`
- * :c:macro:`Py_UNICODE_FILL`
+ * :c:macro:`Py_UNICODE_FILL`: use :c:func:`PyUnicode_Fill`
  * :c:macro:`Py_UNICODE_MATCH`
 
 Encoders: