Bump syn from 1.0.87 to 1.0.88 (#5118)

Bumps [syn](https://github.com/dtolnay/syn) from 1.0.87 to 1.0.88.
- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](https://github.com/dtolnay/syn/compare/1.0.87...1.0.88

)

---
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>