playbook/cpu-scaling-governor: only set governor on online CPUs

prevents vifib.yml playbook from failing for machines containing offline CPUs
8 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed ERP5.StandaloneDeploymentScriptTest-Debian.Bullseye

15:02:19

passed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch

00:39:15

failed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Bullseye

15:02:14

passed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Buster

00:30:03

passed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Stretch

00:57:22

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Bullseye

15:02:12

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

00:27:40

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Stretch

00:39:40