Always have the default workspace in the pg backend

Closes https://github.com/hashicorp/terraform/issues/23121

backend/remote-state/pg/backend_state.go

@@ -10,14 +10,16 @@ import (
 )
 
 func (b *Backend) Workspaces() ([]string, error) {
-	query := `SELECT name FROM %s.%s ORDER BY name`
+	query := `SELECT name FROM %s.%s WHERE name != 'default' ORDER BY name`
 	rows, err := b.db.Query(fmt.Sprintf(query, b.schemaName, statesTableName))
 	if err != nil {
 		return nil, err
 	}
 	defer rows.Close()
 
-	var result []string
+	result := []string{
+		backend.DefaultStateName,
+	}
 
 	for rows.Next() {
 		var name string

backend/remote-state/pg/backend_test.go

@@ -71,6 +71,8 @@ func TestBackendConfig(t *testing.T) {
 	if c.Name != backend.DefaultStateName {
 		t.Fatal("RemoteClient name is not configured")
 	}
+
+	backend.TestBackendStates(t, b)
 }
 
 func TestBackendConfigSkipSchema(t *testing.T) {

backend/testing.go

@@ -94,7 +94,7 @@ func TestBackendStates(t *testing.T, b Backend) {
 
 	// Test it starts with only the default
 	if !noDefault && (len(workspaces) != 1 || workspaces[0] != DefaultStateName) {
-		t.Fatalf("should only default to start: %#v", workspaces)
+		t.Fatalf("should only have the default workspace to start: %#v", workspaces)
 	}
 
 	// Create a couple states