build(deps): update syn requirement from 1.0 to 2.0

Updates the requirements on [syn](https://github.com/dtolnay/syn) to permit the latest version.
- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](dtolnay/syn@1.0.0...2.0.2)

---
updated-dependencies:
- dependency-name: syn
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

attributes/Cargo.toml

@@ -16,7 +16,7 @@ include = ["/src/*", "/Cargo.toml", "/README.md"]
 proc-macro = true
 
 [dependencies]
-syn = { version = "1.0", features = ["full"] }
+syn = { version = "2.0", features = ["full"] }
 quote = "1.0"
 proc-macro2 = "1.0"
 itertools = "0.11"