qapi/schema: add type narrowing to lookup_type()

This function is a bit hard to type as-is; mypy needs some assertions to
assist with the type narrowing.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240315152301.3621858-11-armbru@redhat.com>
1 file changed