ci: cargo_audit job fails due to "proc-macro-error is unmaintained"

The CI fails for a MR with the error:

https://gitlab.torproject.org/opara/arti/-/jobs/662900

$ ./maint/cargo_audit
    Fetching advisory database from `https://github.com/RustSec/advisory-db.git`
      Loaded 655 security advisories (from /usr/local/cargo/advisory-db)
    Updating crates.io index
    Scanning Cargo.lock for vulnerabilities (606 crate dependencies)
Crate:     proc-macro-error
Version:   1.0.4
Warning:   unmaintained
Title:     proc-macro-error is unmaintained
Date:      2024-09-01
ID:        RUSTSEC-2024-0370
URL:       https://rustsec.org/advisories/RUSTSEC-2024-0370
Dependency tree:
proc-macro-error 1.0.4
└── dynasm 2.0.0
    └── dynasmrt 2.0.0
        └── hashx 0.1.5
            └── equix 0.1.7
                └── tor-hspow 0.17.0
error: 1 denied warning found!
Running after_script
Running after script...
$ if command -v cargo && test -d ./target; then cargo clean; fi
/usr/local/cargo/bin/cargo
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1