Update windows compiler to GCC 15

[gitboy16]

Hi @KristofferC ,

I see that you are the last person to have updated the gcc compiler for windows in Artifacts.toml.
Would it be ok to update it to GCC 15?
I guess you are using files from https://github.com/niXman/mingw-builds-binaries ?
I would like to learn/understand how you update these but I don't know how you update the following link:

https://github.com/JuliaLang/PackageCompiler.jl/releases/download/v2.1.24/x86_64-14.2.0-release-posix-seh-msvcrt-rt_v12-rev0.tar.gz

Happy to start a PR if you can guide me.

Thank you

[KristofferC]

I upload the files as a release artifact to GitHub and GitHub generates that link. I will look into updating them to GCC 15, I think it is best that I do it since there is some risk involved with updating a binary blob like this.

[gitboy16]

Ok no problem. Thank you. Please let me know if I can help.