https://github.com/hashicorp/terraform/pull/19389 introduced a change to
the provider GPG signature verification process, and removed the
hardcoded HashiCorp GPG key.
While the changes were intended and are still planned for a future
release, we should still be verifying all providers in the TF 0.12.0
release against the HashiCorp GPG key until a more robust key
verification procedure is in place.
Fixes https://github.com/hashicorp/terraform/issues/20527
