Rust Toolchain Upgrade runs on forks

[Firestar99]

Github just sent me an email about this run failing: https://github.com/jcmnn/rust-gpu/actions/runs/16433959600

Notice how that is a fork of rust-gpu, not the main repo, and for some reason Github still decided to mail me about it? Most likely cause I pushed the last commit to that main branch, since it was used in PR #339.

But if I'm getting emails, other contributors with forks will likely get them as well and annoy them for eternity, or they could just delete the fork... which would be bad for contributions overall.

cc @LegNeato

[LegNeato]

Not near a computer, but I'll fix it later today