.cirrus.yml: Add persistent worker

[bofh]

Summary

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

[bofh]

There are other persistent workers in our pool for docs so isolate
using a different label.

[emaste]

Let's give it a shot!