Support fetching Scala 3 nightlies from new repository

[SethTisue]

since they aren't being published to Maven Central anymore, as per scala/scala3#23761 and other recent tickets

I'm not sure the new repository is 100% up and running yet, but I thought I'd go ahead and open a ticket anyway

cc @hamzaremmal

[hamzaremmal]

@SethTisue Thanks for opening the ticket. I already had a chat about this with @Gedochao and he will implement it after Scala Days.