The build-cortex and build-neuron jobs were running a copied-from-
mistralrs rustup install step. Both jobs use runner images that
already provide rust via dnf:
- runner-rust installs rust/cargo/clippy/rustfmt directly.
- runner-cuda-13.0 extends runner-rust.
Running 'rustup update stable' on top would install a parallel
rustup-managed toolchain and shadow the dnf one — confusing and
unnecessary. The existing ci.yml already trusts the dnf toolchain
without any install step, so match that behaviour.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>