unclosetx: not detect when a function called with a ReadOnlyTransaction argument

[uechoco]

unclosetx cannot detect looks like this sample code.

func f7(ctx context.Context, client *spanner.Client) error {
	ro := client.ReadOnlyTransaction()
	err := Find01(ctx, ro)
	return err
}

func Find01(ctx context.Context, ro *spanner.ReadOnlyTransaction) error {
	row, err := ro.ReadRow(ctx, "DummyTable", spanner.Key{1}, []string{"Id"})
	log.Printf("row: %s", row)
	return err
}