Fix how rustup is verified/installed

[SergioGasquez]

https://github.com/esp-rs/esp-hal/actions/runs/13109391906/job/36569814277?pr=3072 occurred because Rust is not present, its installed by the action but the path is not updated, hence the next steps couldn't find the binary

This didnt occurred in the CI checks of the action as the gh-hosted-runners already have rust installed

esp-hal test: https://github.com/esp-rs/esp-hal/actions/runs/13110802777

[SergioGasquez]

I probably should have looked at dtolnay action, it does it slightly different: https://github.com/dtolnay/rust-toolchain/blob/v1/action.yml#L69-L76, don't think its worth the update but if in the future we want to change it, we could copy it