Run on self-hosted runner with GCS backend

I use a self-hosted Github Actions runner on a VM in GCP that is authorized to my GCS storage backend by its service account. This allows me to run terraform on the VM without providing credentials to access the bucket.

I would like to use the `setup-terraform` step in Github Actions to set up terraform and the wrapper (so the plan can be commented in the PR). I just use:

```
steps:
- uses: hashicorp/setup-terraform@v1
```

This results in an error:

`Error: (s || "").replace is not a function`

I think this is solved when providing specific environment variables with credentials, but I don't want to provide credentials (they should not be needed).