gh-101100: Doc: Suppress sphinx warning in descriptor.rst

Suppress the c:identifier reference warning for 'wrapperbase' by marking it as a literal.

I added the following line at the end of descriptor.rst:

'''
.. c:struct:: wrapperbase

   A structure defining the basic behavior of a descriptor wrapper.
'''

Author: Abhi210

Doc/c-api/descriptor.rst

@@ -38,3 +38,8 @@ found in the dictionary of type objects.
 
 
 .. c:function:: PyObject* PyWrapper_New(PyObject *, PyObject *)
+
+
+.. c:struct:: wrapperbase
+
+   A structure defining the basic behavior of a descriptor wrapper.