.cirrus.yml: Add persistent worker

As we have received an external box sponsored by NetActuate we can now
enable the pre-commit tasks to be run in this box.

Once we have enabled this debug if there are any errors and after
confirmation we can enable this for other tasks too.

Sponsored by: NetActuate
Sponsored by: The FreeBSD Foundation

Approved by: emaste, lwhsu
Differential Revision: https://reviews.freebsd.org/D54220