This warning means nothing, you shouldn’t worry about it since you don’t need to apply any post-processors to the DataSource.
Technically it means that some bean post-processor (a transactional one, I guess) depends on your DataSource, therefore the DataSource must be fully initialized before initialization of that post-processor, so that the post-processor cannot intercept initialization of the DataSource.
You need to worry if you get such a warning about a bean you want to apply post-processors to.