promote cfn2 to ga

[modular-magician]

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• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
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Release Note Template for Downstream PRs (will be copied)

cloudfunction2: promote to `google_cloudfunctions2_function` ga

Derived from GoogleCloudPlatform/magic-modules#6388