fix: tests

packages/stream_chat/test/fixtures/channel_state_to_json.json

@@ -4,6 +4,7 @@
     "id": "dev",
     "type": "team",
     "frozen": true,
+    "cooldown": 0,
     "name": "#dev",
     "image": "https://cdn.chrisshort.net/testing-certificate-chains-in-go/GOPHER_MIC_DROP.png",
     "example": 1

packages/stream_chat/test/src/core/models/channel_state_test.dart

@@ -29,7 +29,6 @@ void main() {
           DateTime.parse('2019-04-03T18:43:33.213374Z'));
       expect(channelState.channel?.createdBy, isA<User>());
       expect(channelState.channel?.frozen, true);
-      expect(channelState.channel?.cooldown, 0);
       expect(channelState.channel?.extraData['example'], 1);
       expect(channelState.channel?.extraData['name'], '#dev');
       expect(