Promote release_channel to GA for GKE

[upodroid]

Fixes: hashicorp/terraform-provider-google#6390

Release Note Template for Downstream PRs (will be copied)

container: added `release_channel` to `google_container-cluster` (GA)

[modular-magician]

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@rileykarson, please review this PR or find an appropriate assignee.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 175 insertions(+))
Terraform Beta: Diff ( 1 file changed, 28 insertions(+), 43 deletions(-))

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 180 insertions(+))
Terraform Beta: Diff ( 1 file changed, 28 insertions(+), 28 deletions(-))

[rileykarson]

Thanks @upodroid!

[nat-henderson]

I'm suspicious that this change broke the GKE tests.

https://ci-oss.hashicorp.engineering/buildConfiguration/GoogleCloud_ProviderGoogleCloudMmUpstreamVcr/138115

[nat-henderson]

I think you need a nil check here before the attempt at a cast; if l == nil { return nil }.

[rileykarson]

Oh whoops, I forgot that VCR doesn't run on community PRs. Makes sense! I see you sent #3836.

[upodroid]

Hi, was it broken in the beta one too?

[nat-henderson]

It didn't seem to be, which is a little odd! I am waiting for the tests to come back to be sure that this is the issue.