bug#64297: [Cuirass] Remote server not picking up job, losing workers

[Ludovic Courtès]

As of cuirass@1.1.0-16.b825967, ‘cuirass remote-server’ appears to not
pick jobs as quickly as it should and to lose sight of workers (you can
see them come and go on <https://ci.guix.gnu.org/workers>).

/var/log/cuirass-remote-worker.log shows that it does build things, but
only sporadically.  Then there are things like:

  2023-06-26 10:07:58 warning: Poll loop busy during 3404 seconds.

This is presumably related to Cuirass commit
c4743b54720e86b0e0b0295fb6d33977e4293644 (previously ‘remote-worker’
would have a database worker thread; now it opens a new connection every
time—a stopgap before it’s fiberized, but apparently not a good one).

Ludo’.