Migrate CI event listener to v1beta1

All trigger resources are still v1alpha1.
Migrating the CI event listener for now since it's required by
for trigger groups: #956

Signed-off-by: Andrea Frittoli <andrea.frittoli@uk.ibm.com>

tekton/ci/shared/eventlistener.yaml

@@ -1,5 +1,5 @@
 ---
-apiVersion: triggers.tekton.dev/v1alpha1
+apiVersion: triggers.tekton.dev/v1beta1
 kind: EventListener
 metadata:
   name: tekton-ci