bpo-16086: Fix PyType_GetFlags() documentation (GH-10758)

PyType_GetFlags() return type is unsigned long, not long.

Doc/c-api/type.rst

@@ -35,7 +35,7 @@ Type Objects
 
    Clear the internal lookup cache. Return the current version tag.
 
-.. c:function:: long PyType_GetFlags(PyTypeObject* type)
+.. c:function:: unsigned long PyType_GetFlags(PyTypeObject* type)
 
    Return the :c:member:`~PyTypeObject.tp_flags` member of *type*. This function is primarily
    meant for use with `Py_LIMITED_API`; the individual flag bits are
@@ -44,6 +44,9 @@ Type Objects
 
    .. versionadded:: 3.2
 
+   .. versionchanged:: 3.4
+      The return type is now ``unsigned long`` rather than ``long``.
+
 
 .. c:function:: void PyType_Modified(PyTypeObject *type)