Fix parseResponse() to use explicit UTF-8 charset

Prevents platform-dependent test failures on non-UTF-8 systems
(e.g., Windows with windows-1252 default). Consistent with the
existing toString("UTF-8") call at line 111.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: robertlazarski

modules/json/test/org/apache/axis2/json/streaming/FieldFilteringMessageFormatterTest.java

@@ -346,7 +346,12 @@ private void setReturnObject(Object obj) {
     }
 
     private JsonElement parseResponse() {
-        String json = outputStream.toString();
+        String json;
+        try {
+            json = outputStream.toString("UTF-8");
+        } catch (java.io.UnsupportedEncodingException e) {
+            throw new AssertionError("UTF-8 encoding not supported", e);
+        }
         JsonElement root = JsonParser.parseString(json);
         return root.getAsJsonObject().get("response");
     }