test: generated_serializer: Test enum that is struct member

Add an enum field to the test struct member to test
serialization/deserialization of enums that are struct members.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

test/serialization/generated_serializer/include/libcamera/ipa/test.mojom

@@ -18,6 +18,7 @@ struct TestStruct {
 	string s2;
 	int32 i;
 	string s3;
+	IPAOperationCode c;
 };
 
 interface IPATestInterface {