bpo-45476: Add _Py_RVALUE() macro (GH-29860)

bpo-45476: Add _Py_RVALUE() macro (GH-29860)

Add a new _Py_RVALUE() macro to prevent using an expression as an
l-value.

Replace a "(void)" cast with the _Py_RVALUE() macro in the following
macros:

* PyCell_SET()
* PyList_SET_ITEM()
* PyTuple_SET_ITEM()
* _PyGCHead_SET_FINALIZED()
* _PyGCHead_SET_NEXT()
* asdl_seq_SET()
* asdl_seq_SET_UNTYPED()

Add also parentheses around macro arguments in PyCell_SET() and
PyTuple_SET_ITEM() macros.