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...2.0.3)

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

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

Author: dependabot[bot]

postgres-derive/Cargo.toml

@@ -12,6 +12,6 @@ proc-macro = true
 test = false
 
 [dependencies]
-syn = "1.0"
+syn = "2.0"
 proc-macro2 = "1.0"
 quote = "1.0"