proc-macro-error is unmaintained

[jayvdb]

c.f. rustsec/advisory-db#2057

utoipa> osv-scanner --lockfile Cargo.lock
Scanned /home/jayvdb/rust/utoipa/Cargo.lock file and found 344 packages
╭───────────────────────────────────┬──────┬───────────┬──────────────────┬─────────┬────────────╮
│ OSV URL                           │ CVSS │ ECOSYSTEM │ PACKAGE          │ VERSION │ SOURCE     │
├───────────────────────────────────┼──────┼───────────┼──────────────────┼─────────┼────────────┤
│ https://osv.dev/RUSTSEC-2024-0370 │      │ crates.io │ proc-macro-error │ 1.0.4   │ Cargo.lock │
╰───────────────────────────────────┴──────┴───────────┴──────────────────┴─────────┴────────────╯

[jayvdb]

https://github.com/GnomedDev/proc-macro-error-2 is the recommended alternative

[jayvdb]

proc-macro-error-2 requires using syn 2, so #7 is a necessary step

[Electron100]

@nvksv any chance you'd be able to release a 0.2.5 version with this fix?