Change unmaintained proc-macro-error dependency

[nejcgalof]

Currently, that crate relies on the unmaintained proc-macro-error, which we can detect as a problem with some tools, for example cargo deny.
With that particular tool, we get the following output:

error[unmaintained]: proc-macro-error is unmaintained
    ┌─ /code/Cargo.lock:162:1
    │
162 │ proc-macro-error 1.0.4 registry+https://github.com/rust-lang/crates.io-index
    │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ unmaintained advisory detected
    │
    ├ ID: RUSTSEC-2024-0370
    ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2024-0370
    ├ proc-macro-error's maintainer seems to be unreachable, with no commits for 2 years, no releases pushed for 4 years, and no activity on the GitLab repo or response to email.
      
      proc-macro-error also depends on `syn 1.x`, which may be bringing duplicate dependencies into dependant build trees.
      
      ## Possible Alternative(s)
      
      - [manyhow](https://crates.io/crates/manyhow)
      - [proc-macro-error2](https://crates.io/crates/proc-macro-error2)
      - [proc-macro2-diagnostics](https://github.com/SergioBenitez/proc-macro2-diagnostics)
    ├ Announcement: https://gitlab.com/CreepySkeleton/proc-macro-error/-/issues/20
    ├ Solution: No safe upgrade is available!
    ├ proc-macro-error v1.0.4
      └── statig_macro v0.3.0
          └── statig v0.3.0

More about that: https://rustsec.org/advisories/RUSTSEC-2024-0370

The proc-macro-error2 is just forked from the unmaintained proc-macro-error. It may be good to change that dependency and update others.

[mdeloof]

Thanks for pointing this out. I'll try to find a solution for the upcoming 0.4 release.