Fix CGLibProxySerializerTest after upgrade to kryo 2.24.0

Since 2.24.0 the instantiation strategy has to be used differently,
basically the DefaultInstatiatorStrategy with StdInstantiatorStrategy
as fallback should be used.
The test failed, because just the StdInstantiatorStrategy was used
and this created the HashMap via Reflection, so that the HashMap was
not properly initialized.