Provider doesn't gracefully handle 404 for env group

[bdewater-thatch]

While messing around for #56 it seems I badly broke things when I deleted everything from the Render dashboard, but still have local Terraform state. It correctly detects things have changed outside of TF and everything needs recreating (services, DBs, ENV vars) except for the env group itself, I get this error when planning:

Plan: 5 to add, 0 to change, 0 to destroy.
╷
│ Error: unable to get environment group
│ 
│   with module.thatch_app.render_env_group_link.thatch,
│   on ../../modules/thatch-app/main.tf line 156, in resource "render_env_group_link" "thatch":
│  156: resource "render_env_group_link" "thatch" {
│ 
│ unexpected status: 404 Not Found
╵
2025-06-16T16:47:18.005-0400 [DEBUG] provider.stdio: received EOF, stopping recv loop: err="rpc error: code = Unavailable desc = error reading from server: EOF"
2025-06-16T16:47:18.006-0400 [DEBUG] provider: plugin process exited: path=.terraform/providers/registry.terraform.io/render-oss/render/1.7.0/darwin_arm64/terraform-provider-render_v1.7.0 pid=67155
2025-06-16T16:47:18.006-0400 [DEBUG] provider: plugin exited

Deleting my tfstate files and planning again:

Plan: 6 to add, 0 to change, 0 to destroy.

without errors.