Update loongarch64 release builds to use `gcc-loongarch64-linux-gnu` package

[casey]

From https://github.com/casey/just/pull/2886#issuecomment-3448010454:

gcc-loongarch64-linux-gnu is a metapackage that points to a specific version of GCC, e.g., in Ubuntu 24.10/25.04, it points to gcc-14 loongarch64-linux-gnu. However, the latest Ubuntu version of GitHub Actions is currently 24.04, and the metapackage gcc-loongarch64-linux-gnu doesn't exist in this version, so we have to use gcc-$VERSION-loongarch64-linux-gnu instead.

Switch from gcc-14 loongarch64-linux-gnu to gcc-loongarch64-linux-gnu once Github Actions linux runners update to Ubuntu 24.10.