fix api-gateway import tests

[modular-magician]

closes hashicorp/terraform-provider-google#9789
closes hashicorp/terraform-provider-google#9782
closes hashicorp/terraform-provider-google#9785

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Release Note Template for Downstream PRs (will be copied)

apigateway: fixed import functionality for all `apigateway` resources

Derived from GoogleCloudPlatform/magic-modules#5104