ci: Run GKE jobs only on gke nodes

We are isolating this job to separate node pool which will have multiple
executors, so we don't lock regular baremetal nodes needed for builds
using vagrant

Signed-off-by: Maciej Kwiek <maciej@isovalent.com>

jenkinsfiles/ginkgo-gke.Jenkinsfile

@@ -2,7 +2,7 @@
 
 pipeline {
     agent {
-        label 'baremetal'
+        label 'gke'
     }
 
     environment {