bpo-40170: Fix PyType_Ready() refleak on static type (GH-23236)

bpo-1635741, bpo-40170: When called on a static type with NULL
tp_base, PyType_Ready() no longer increments the reference count of
the PyBaseObject_Type ("object). PyTypeObject.tp_base is a strong
reference on a heap type, but it is borrowed reference on a static
type.

Fix 99 reference leaks at Python exit (showrefcount 18623 => 18524).
diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index ec6a364..43b0be3 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -244,6 +244,7 @@ struct _typeobject {
     struct PyMethodDef *tp_methods;
     struct PyMemberDef *tp_members;
     struct PyGetSetDef *tp_getset;
+    // Strong reference on a heap type, borrowed reference on a static type
     struct _typeobject *tp_base;
     PyObject *tp_dict;
     descrgetfunc tp_descr_get;