Make Rust CI action zizmor compliant

[emmatyping]

CPython has adopted zizmor, and since we have added an action, we should make it compliant with zizmor.

Currently failing job log: https://github.com/Rust-for-CPython/cpython/actions/runs/29635827292/job/88057864868

The documentation for zizmor is here: https://docs.zizmor.sh/