indeed, that

WithSystemCerts

started returning an error recently, so the code would look like this:

func main() {
    systemCerts, err := grpcutil.WithSystemCerts(grpcutil.VerifyCA)
    if err != nil {
        log.Fatalf("unable to load system certs: %s", err)
    }

    client, err := authzed.NewClient(
        "grpc.authzed.com:443",
        grpcutil.WithBearerToken("t_your_token_here_1234567deadbeef"),
        systemCerts,
    )
    if err != nil {
        log.Fatalf("unable to initialize client: %s", err)
    }

    request := &pb.WriteSchemaRequest{Schema: schema}
    _, err = client.WriteSchema(context.Background(), request)
    if err != nil {
        log.Fatalf("failed to write schema: %s", err)
    }
}