Consider updating rstest_macros to use Syn v2

[LikeLakers2]

Hi! Syn v2 recently released. However, I notice you're still using Syn v1. Perhaps you could consider updating rstest_macros to use Syn v2?

Something to consider before doing so: Syn v2's new MSRV is Rust 1.56, moved up from Rust 1.31. Rust 1.56 was released in October 2021, making it a relatively old version. However, rstest does not appear to have an MSRV, not even with the rust-version Cargo.toml option - so I'm unsure what MSRV you intend rstest to have.

You may also have to edit some code to support some of the breaking changes that Syn v2 brings with it.

However, if neither of those are a problem to you, then consider changing your Syn dependency to depend on Syn v2.

[la10736]

Thx to report it. I'll do some experiments ASAP and 1.56 it's ok as MSRV. I don't think that the syn breaking changes can be an issue and maybe I'll also switch to 2021 edition.