NRPE check check-ntpmon fails

[Bas de Bruijne]

In testrun https://solutions.qa.canonical.com/v2/testruns/8e7c2530-9cd7-4d87-a7d6-aa51ff91d370, the check-ntpmon test fails with:

```
- check: check-ntpmon
  id: '154'
  results:
    check-output: 'CRITICAL: No sync peer selected | frequency=-5.648000 offset=-0.000029
      peers=20 reach=100.000000 result=2 rootdelay=0.085089 rootdisp=0.036175 runtime=1448
      stratum=4 sync=0.000000 sysjitter= sysoffset=0.000013675 tracehosts= traceloops=
      tracetime='
    return-code: 0
  status: completed
  timing:
    completed: 2023-01-26 15:41:37 +0000 UTC
    enqueued: 2023-01-26 15:41:35 +0000 UTC
    started: 2023-01-26 15:41:36 +0000 UTC
  unit: nrpe/5
```

The ntp logs don't indicate any failures, I'm not sure why this is happening.

The crashdump can be found here: https://oil-jenkins.canonical.com/artifacts/8e7c2530-9cd7-4d87-a7d6-aa51ff91d370/index.html