Unit tests: run on CERN runners

The CERN runners have way more CPU cores, which speeds up our unit tests
heavily. Previously we had to filter which OSes we test on, this can be
removed now.

Author: bastelfreak

.github/workflows/ci.yml

@@ -21,3 +21,4 @@ jobs:
     uses: voxpupuli/gha-puppet/.github/workflows/beaker.yml@v2
     with:
       beaker_facter: 'zabbix_version:Zabbix:5.0,6.0,7.0'
+      unit_runs_on: 'cern-self-hosted'

.sync.yml

@@ -15,3 +15,4 @@ spec/spec_helper.rb:
 .github/workflows/ci.yml:
   with:
     beaker_facter: 'zabbix_version:Zabbix:5.0,6.0'
+    unit_runs_on: 'cern-self-hosted'