Default workspace is listed twice when using etcdv3 backend

[jasons42]

Terraform Version

v0.14.8

Terraform Configuration Files

  backend "etcdv3" {
    endpoints   = ["localhost:2379"]
    prefix      = "test-tf/"
    lock        = true
  }

  required_version = ">= 0.13"
}

Command Output

terraform workspace list 
* default
* default

Expected Behavior

Default workspace should be listed once.

Actual Behavior

Default workspace is listed twice.

Steps to Reproduce

1. Configure a Terraform config to use the etcdv3 backend
2. terraform workspace list

Additional Context

This is also caught by the acceptance tests after applying a fix for #28096

TF_ACC=1 TF_ETCDV3_ENDPOINTS=http://127.0.0.1:2379 go test ./backend/remote-state/etcdv3
--- FAIL: TestBackend (0.25s)
    backend_test.go:40: Cleaned up 0 keys.
    backend_test.go:62: TestBackendConfig on *etcd.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"endpoints":cty.TupleVal([]cty.Value{cty.StringVal("http://127.0.0.1:2379")}), "prefix":cty.StringVal("tf-unit/2021-03-15T16:30:34-05:00/")}}
    backend_test.go:67: TestBackendConfig on *etcd.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"endpoints":cty.TupleVal([]cty.Value{cty.StringVal("http://127.0.0.1:2379")}), "prefix":cty.StringVal("tf-unit/2021-03-15T16:30:34-05:00/")}}
    backend_test.go:73: should only have the default workspace to start: []string{"default", "default"}
    backend_test.go:40: Cleaned up 1 keys.
FAIL
FAIL    github.com/hashicorp/terraform/backend/remote-state/etcdv3      4.543s
FAIL

[ghost]

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