update gcm_channel upsert schema

[LiamAttClarke]

Description

Relations

Closes #0000

References

Output from Acceptance Testing

% make testacc TESTS=TestAccXXX PKG=ec2

...

#35261

[github-actions]

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[github-actions]

Welcome @LiamAttClarke 👋

It looks like this is your first Pull Request submission to the Terraform AWS Provider! If you haven’t already done so please make sure you have checked out our CONTRIBUTOR guide and FAQ to make sure your contribution is adhering to best practice and has all the necessary elements in place for a successful approval.

Also take a look at our FAQ which details how we prioritize Pull Requests for inclusion.

Thanks again, and welcome to the community! 😃