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).