[app_rx] fix min deps

app_rx/pubspec.yaml

@@ -7,7 +7,7 @@ environment:
   sdk: '>=3.3.0 <4.0.0'
 
 dependencies:
-  rxdart: '>=0.27.7'
+  rxdart: '>=0.28.0'
   tekartik_common_utils:
     git:
       url: https://github.com/tekartik/common_utils.dart