fix ClassCastException

Author: leyou240

dubbo-metrics/dubbo-tracing/src/main/java/org/apache/dubbo/tracing/handler/DubboClientTracingObservationHandler.java

@@ -35,6 +35,6 @@ public void onScopeOpened(T context) {}
 
     @Override
     public boolean supportsContext(Observation.Context context) {
-        return context instanceof SenderContext;
+        return context instanceof DubboClientContext;
     }
 }

dubbo-metrics/dubbo-tracing/src/main/java/org/apache/dubbo/tracing/handler/DubboServerTracingObservationHandler.java

@@ -46,6 +46,6 @@ public void onScopeOpened(T context) {
 
     @Override
     public boolean supportsContext(Observation.Context context) {
-        return context instanceof ReceiverContext;
+        return context instanceof DubboServerContext;
     }
 }