GCP discovery can't enroll instances

[r0mant]

Given the following discovery config:

discovery_service:
  enabled: "yes"
  gcp:
    - types: ["gce"]
      project_ids: ["<redacted>"]
      locations: ["us-central1-a"]
      tags:
        "project": "*"

User is seeing the following error in the logs:

2023-09-01T21:24:49Z DEBU [DISCOVERY] GCP instances discovered (ProjectID: <REDACTED>, Instances [teleport-discovery-node]), starting installation pid:2919.1 discovery/discovery.go:737
2023-09-01T21:24:49Z DEBU [DISCOVERY] Running Teleport installation on these virtual machines: ProjectID: <REDACTED>, VMs: [teleport-discovery-node] pid:2919.1 discovery/discovery.go:712
2023-09-01T21:24:49Z ERRO [DISCOVERY] Failed to enroll discovered GCP VMs. error:[
ERROR REPORT:
Original Error: *trace.BadParameterError 
Stack Trace:

Caught:
	github.com/gravitational/teleport/lib/cloud/gcp/vm.go:52 github.com/gravitational/teleport/lib/cloud/gcp.convertAPIError
	github.com/gravitational/teleport/lib/cloud/gcp/vm.go:304 github.com/gravitational/teleport/lib/cloud/gcp.(*instancesClient).GetInstance
	github.com/gravitational/teleport/lib/cloud/gcp/vm.go:498 github.com/gravitational/teleport/lib/cloud/gcp.RunCommand
	github.com/gravitational/teleport/lib/srv/server/gcp_installer.go:69 github.com/gravitational/teleport/lib/srv/server.(*GCPInstaller).Run.func1
	golang.org/x/[email protected]/errgroup/errgroup.go:75 golang.org/x/sync/errgroup.(*Group).Go.func1
	runtime/asm_amd64.s:1598 runtime.goexit
User Message: Invalid resource field value in the request.

Seems like this GetInstance call is failing for some reason.