ubuntu-gcc12 update gcc?

On [the website](https://r-hub.github.io/containers/) it is noted that `ubuntu-gcc12` is equivalent to `r-devel-linux-x86_64-debian-gcc`, but looking at https://cran.r-project.org/web/checks/check_flavors.html it looks like `r-devel-linux-x86_64-debian-gcc` is on GCC 15 these days. I suspect it might be "just" updating https://github.com/r-hub/containers/blob/1033a790e20c701a8cb424bc077faf4956285a9f/containers/ubuntu-gcc12/Dockerfile#L24-L35 Or maybe it makes sense to make a separate ubuntu-gcc15? I'm happy to give that a go if you're open to it.