Bump syn from 2.0.28 to 2.0.29 (#3053)

Bumps [syn](https://github.com/dtolnay/syn) from 2.0.28 to 2.0.29.
- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](dtolnay/syn@2.0.28...2.0.29)

---
updated-dependencies:
- dependency-name: syn
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

cumulus/Cargo.lock

@@ -9,7 +9,7 @@ description = "Proc macros provided by the parachain-system pallet"
 proc-macro = true
 
 [dependencies]
-syn = "2.0.28"
+syn = "2.0.29"
 proc-macro2 = "1.0.64"
 quote = "1.0.33"
 proc-macro-crate = "1.3.1"