build(deps): bump syn from 1.0.63 to 1.0.64
Bumps [syn](https://github.com/dtolnay/syn) from 1.0.63 to 1.0.64.
- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](https://github.com/dtolnay/syn/compare/1.0.63...1.0.64)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>