fix(spanner): fix escaping of database name in spanner ddl with POSTGRES dialect

[modular-magician]

Currently name attribute having - in value cannot be populated because of issue in escaping database name
e.g

variables "database_name" {
type = string
default = "dbatest5-postgres"
}

resource "google_spanner_database" "database" {
instance = google_spanner_instance.main.name
name = ""${var.database_name}""
database_dialect = "POSTGRESQL"
deletion_protection = false
}

This PR will fix the escaping with POSTGRES dialect

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spanner: fix escaping of database names with Postgres dialect in `google_spanner_database`

Derived from GoogleCloudPlatform/magic-modules#5938