:pep:`612` is now implemented purely in Python; builtin ``types.GenericAlias``
objects no longer include ``typing.ParamSpec`` in ``__parameters__``
(with the exception of ``collections.abc.Callable``\ 's ``GenericAlias``).
This means previously invalid uses of ``ParamSpec`` (such as
``list[P]``) which worked in earlier versions of Python 3.10 alpha,
will now raise ``TypeError`` during substitution.
