`@rustbot note`: Allow for multiple note entries in the same comment

[chazkiker2]

[chazkiker2]

@Mark-Simulacrum is this something we should be supporting? Or do we think it's appropriate to only contain one note per comment?

[Mark-Simulacrum]

I think we should try to support this -- I could see it being useful. If the impl is pretty easy (IIRC, we try to support this for some other commands, or maybe I just hoped that we would) -- then we definitely should, but I would not try to majorly refactor code to handle this case.