testing: Move bulk of GCP-Auth addon test into subtest #12302

Job	Run time
build_minikube	7m 35s
build_minikube_test_binaries	3m 21s
lint	2m 28s
unit_test	1m 7s
functional_podman_ubuntu	9m 33s
functional_docker_containerd_ubuntu	7m 4s
functional_docker_rootless_containerd_ubuntu	8m 45s
functional_baremetal_ubuntu22_04	5m 19s
functional_docker_ubuntu	6m 24s
upload_all_reports	7s
	51m 43s

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