Fix TestAccContainerCluster_withConfidentialNodes

[c2thorn]

Test misconfiguration:

Error: googleapi: Error 400: Master version must be one of "RAPID" channel supported versions [1.18.12-gke.1200, 1.18.12-gke.1201]., badRequest

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 hashibot-feedback@hashicorp.com. Thanks!