Bump syn from 2.0.28 to 2.0.29

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]>

Author: dependabot[bot]