fix: install auth plugin on gke environment tests (#1232)

* install auth plugin on gke environment tests * 🦉 Updates from OwlBot post-processor See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: daniel-sanche

.kokoro/environment_tests.sh

@@ -63,6 +63,9 @@ if [[ "${ENVIRONMENT}" == "kubernetes" ]]; then
  mkdir -p ~/.local/bin
  mv ./kubectl ~/.local/bin
  export PATH=$PATH:~/.local/bin
+ # install auth plugin
+ gcloud components install gke-gcloud-auth-plugin -q
+ export USE_GKE_GCLOUD_AUTH_PLUGIN=True
 fi
 
 # create a unique id for this run