Use reset flash for includes as well. Fixes #9370

Author: graemerocher

grails-web-mvc/src/main/groovy/org/grails/web/servlet/mvc/GrailsWebRequestFilter.java

@@ -62,7 +62,7 @@ protected void doFilterInternal(HttpServletRequest request, HttpServletResponse
         try {
             WebUtils.storeGrailsWebRequest(webRequest);
 
-            if(!WebUtils.isForward(request)) {
+            if(!WebUtils.isForwardOrInclude(request)) {
                 // Set the flash scope instance to its next state. We do
                 // this here so that the flash is available from Grails
                 // filters in a valid state.