fix(alertcenter): update the API

#### alertcenter:v1beta1

The following keys were changed:
- schemas.Empty.description

discovery/alertcenter-v1beta1.json

@@ -423,7 +423,7 @@
       }
     }
   },
-  "revision": "20220307",
+  "revision": "20220321",
   "rootUrl": "https://alertcenter.googleapis.com/",
   "schemas": {
     "AccountSuspensionDetails": {
@@ -1086,7 +1086,7 @@
       "type": "object"
     },
     "Empty": {
-      "description": "A generic empty message that you can re-use to avoid defining duplicated empty messages in your APIs. A typical example is to use it as the request or the response type of an API method. For instance: service Foo { rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty); } The JSON representation for `Empty` is empty JSON object `{}`.",
+      "description": "A generic empty message that you can re-use to avoid defining duplicated empty messages in your APIs. A typical example is to use it as the request or the response type of an API method. For instance: service Foo { rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty); }",
       "id": "Empty",
       "properties": {},
       "type": "object"

src/apis/alertcenter/v1beta1.ts

@@ -596,7 +596,7 @@ export namespace alertcenter_v1beta1 {
     takeoutRequestId?: string | null;
   }
   /**
-   * A generic empty message that you can re-use to avoid defining duplicated empty messages in your APIs. A typical example is to use it as the request or the response type of an API method. For instance: service Foo { rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty); \} The JSON representation for `Empty` is empty JSON object `{\}`.
+   * A generic empty message that you can re-use to avoid defining duplicated empty messages in your APIs. A typical example is to use it as the request or the response type of an API method. For instance: service Foo { rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty); \}
    */
   export interface Schema$Empty {}
   /**