Add dubbo package to serialize allow list for SpringXmlConfigTest to avoid IllegalArgumentException (#15714)

Author: zrlw

dubbo-test/dubbo-test-spring/src/main/resources/security/serialize.allowlist

@@ -0,0 +1,20 @@
+#
+#
+#   Licensed to the Apache Software Foundation (ASF) under one or more
+#   contributor license agreements.  See the NOTICE file distributed with
+#   this work for additional information regarding copyright ownership.
+#   The ASF licenses this file to You under the Apache License, Version 2.0
+#   (the "License"); you may not use this file except in compliance with
+#   the License.  You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
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+#
+#
+
+org.apache.dubbo