Update syn requirement from 1.0.90 to 2.0.13

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@1.0.90...2.0.13)

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

Signed-off-by: dependabot[bot] <support@github.com>

juniper_codegen/Cargo.toml

@@ -25,7 +25,7 @@ proc-macro = true
 proc-macro-error = "1.0.2"
 proc-macro2 = "1.0.4"
 quote = "1.0.9"
-syn = { version = "1.0.90", features = ["extra-traits", "full", "parsing", "visit", "visit-mut"], default-features = false }
+syn = { version = "2.0.13", features = ["extra-traits", "full", "parsing", "visit", "visit-mut"], default-features = false }
 url = "2.0"
 
 [dev-dependencies]