fix: missing internal imports for python serialization

Signed-off-by: Vincent Biret <vibiret@microsoft.com>

src/Kiota.Builder/Writers/Python/CodeMethodWriter.cs

@@ -646,6 +646,7 @@ private void WriteSerializerBodyForInheritedModel(bool inherits, CodeClass paren
     {
         if (inherits)
             writer.WriteLine("super().serialize(writer)");
+        _codeUsingWriter.WriteInternalImports(parentClass, writer);
         foreach (var otherProp in parentClass
                                         .GetPropertiesOfKind(CodePropertyKind.Custom)
                                         .Where(static x => !x.ExistsInBaseType && !x.ReadOnly)