Fix the 3rd occurence of old ig instances interpolation syntax (#3142)
Fix the 3rd occurence of old ig instances interpolation syntax (#3142)

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/cc @rileykarson
ubschmidt2/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,terraform-providers/terraform-provider-google,ubschmidt2/terraform-provider-google,ubschmidt2/terraform-provider-google,hashicorp/terraform-provider-google,terraform-providers/terraform-provider-google,hashicorp/terraform-provider-google,hashicorp/terraform-provider-google,ubschmidt2/terraform-provider-google