apply texttheme to rest of headers

packages/stream_chat_flutter/lib/src/channel_list_header.dart

@@ -120,6 +120,7 @@ class ChannelListHeader extends StatelessWidget implements PreferredSizeWidget {
           showMessage: showConnectionStateTile ? showStatus : false,
           message: statusString,
           child: AppBar(
+            textTheme: Theme.of(context).textTheme,
             brightness: Theme.of(context).brightness,
             elevation: 1,
             backgroundColor: chatThemeData.channelListHeaderTheme.color,

packages/stream_chat_flutter/lib/src/image_header.dart

@@ -53,6 +53,7 @@ class ImageHeader extends StatelessWidget implements PreferredSizeWidget {
   Widget build(BuildContext context) {
     final chatThemeData = StreamChatTheme.of(context);
     return AppBar(
+      textTheme: Theme.of(context).textTheme,
       brightness: Theme.of(context).brightness,
       elevation: 1,
       leading: showBackButton

packages/stream_chat_flutter/lib/src/thread_header.dart

@@ -101,6 +101,7 @@ class ThreadHeader extends StatelessWidget implements PreferredSizeWidget {
     final chatThemeData = StreamChatTheme.of(context);
     return AppBar(
       automaticallyImplyLeading: false,
+      textTheme: Theme.of(context).textTheme,
       brightness: Theme.of(context).brightness,
       elevation: 1,
       leading: leading ??