ci: Ensure macOS builds use same technique for updating stable
ci: Ensure macOS builds use same technique for updating stable

Linux builds had stable update action steps, but for some reason
macOS was lacking them. This sorts that out.

Signed-off-by: Daniel Silverstone <3cc17a76d780e0cd3d87bad586a1c53967be5625@digital-scurf.org>

rust-lang/rustup,nodakai/rustup.rs,inejge/rustup.rs,rust-lang/rustup,inejge/rustup.rs,inejge/rustup.rs,nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,nodakai/rustup.rs,nodakai/rustup.rs,inejge/rustup.rs,rust-lang/rustup,inejge/rustup.rs,rust-lang/rustup