Updated Ruby conformance test failure list

This commit adds two entries to the conformance failure list for Ruby.
It seems that these particular test cases have been failing since they
were introduced in 5140bae3834c40208e44b1eeb947485a832387a7, so there
has not been any regression.

conformance/failure_list_ruby.txt

@@ -120,6 +120,8 @@ Required.Proto3.JsonInput.ValueAcceptInteger.JsonOutput
 Required.Proto3.JsonInput.ValueAcceptInteger.ProtobufOutput
 Required.Proto3.JsonInput.ValueAcceptList.JsonOutput
 Required.Proto3.JsonInput.ValueAcceptList.ProtobufOutput
+Required.Proto3.JsonInput.ValueAcceptListWithNull.JsonOutput
+Required.Proto3.JsonInput.ValueAcceptListWithNull.ProtobufOutput
 Required.Proto3.JsonInput.ValueAcceptNull.JsonOutput
 Required.Proto3.JsonInput.ValueAcceptNull.ProtobufOutput
 Required.Proto3.JsonInput.ValueAcceptObject.JsonOutput