Interpolation-only expressions are deprecated warning

[jdyke]

Terraform is giving off a warning which fails some CI checks when running terraform plan via GitHub actions. We no longer need to specify ${}for expressions in >=12 .

terraform-google-event-function/main.tf

Line 36 in 76efb3a

dependent_files_id = "${null_resource.dependent_files.id}"

I'll create a PR to address this shortly but wanted an issue first.