message: fix(ts): fix getPolicy promise return signature
diff: @@ -176,7 +176,7 @@ export class IAM {
  this.id = id;
  }
  - getPolicy(gaxOpts?: CallOptions): Promise<GetPolicyCallback>;
  + getPolicy(gaxOpts?: CallOptions): Promise<GetPolicyResponse>;
  getPolicy(callback: GetPolicyCallback): void;
  getPolicy(gaxOpts: CallOptions, callback: GetPolicyCallback): void;
  /**
  @@ -211,7 +211,7 @@ export class IAM {
  */
  getPolicy(
  gaxOptsOrCallback?: CallOptions|GetPolicyCallback,
  - callback?: GetPolicyCallback): Promise<GetPolicyCallback>|void {
  + callback?: GetPolicyCallback): Promise<GetPolicyResponse>|void {
  const gaxOpts =
  typeof gaxOptsOrCallback === 'object' ? gaxOptsOrCallback : {};
  callback =
  