[SBISSUE-18723] Fix undefined error in MessageList (#1318)

### Ticket
[SBISSUE-18723](https://sendbird.atlassian.net/browse/SBISSUE-18723)

### Changelog
* Fix undefined error in MessageList.

[SBISSUE-18723]:
https://sendbird.atlassian.net/browse/SBISSUE-18723?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: git-babel

src/modules/GroupChannel/__test__/MessageList.integration.test.tsx

@@ -0,0 +1,22 @@
+import React from 'react';
+import { render } from '@testing-library/react';
+import '@testing-library/jest-dom/extend-expect';
+import MessageList from '../components/MessageList';
+import { GroupChannelProvider } from '../context';
+import SendbirdProvider from '../../../lib/Sendbird/context/SendbirdProvider';
+
+describe('MessageList Unit Tests', () => {
+  const defaultProps = {
+    channelUrl: 'test-channel',
+  };
+
+  it('renders MessageList with default value', () => {
+    render(
+      <SendbirdProvider appId="mockAppId" userId="mockUserId">
+        <GroupChannelProvider {...defaultProps}>
+          <MessageList />
+        </GroupChannelProvider>,
+      </SendbirdProvider>,
+    );
+  });
+});

src/modules/GroupChannel/context/GroupChannelProvider.tsx

@@ -39,6 +39,7 @@ const initialState = {
   fetchChannelError: null,
   nicknamesMap: new Map(),
 
+  messages: [],
   quoteMessage: null,
   animatedMessageId: null,
   isScrollBottomReached: true,