qapi/schema: turn on mypy strictness This patch can be rolled in with the previous one once the series is ready for merge, but for work-in-progress' sake, it's separate here. 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: <20240315152301.3621858-23-armbru@redhat.com>