correct invalid test data

Original data accepted only because of extra suds logic to support invalid XSD
schemas but neither was the data actually a valid XSD schema nor is testing that
logic the purpose of the test in question.

tests/test_request_construction.py

@@ -440,7 +440,7 @@ def test_element_references_to_different_namespaces():
         <xsd:complexType>
           <xsd:sequence>
             <xsd:element name="local" type="xsd:string"/>
-            <xsd:element ref="local_referenced"/>
+            <xsd:element ref="tns:local_referenced"/>
             <xsd:element ref="second:external"/>
           </xsd:sequence>
         </xsd:complexType>