[Python] Verify EnumDef is not generated in GenUnionCreator (#6903)

* [Python] Verify EnumDef is not generated in GenUnionCreator

* update test output

src/idl_gen_python.cpp

@@ -1595,6 +1595,8 @@ class PythonGenerator : public BaseGenerator {
 
   // Creates an union object based on union type.
   void GenUnionCreator(const EnumDef &enum_def, std::string *code_ptr) {
+    if (enum_def.generated) return;
+
     auto &code = *code_ptr;
     auto union_name = MakeUpperCamel(enum_def);
 

tests/namespace_test/NamespaceA/NamespaceB/UnionInNestedNS.py

@@ -2,6 +2,10 @@
 
 # namespace: NamespaceB
 
+class UnionInNestedNS(object):
+    NONE = 0
+    TableInNestedNS = 1
+
 
 def UnionInNestedNSCreator(unionType, table):
     from flatbuffers.table import Table