build(deps): bump third_party/tools/synlig from bd35861 to c68d684

Bumps [third_party/tools/synlig](https://github.com/chipsalliance/synlig) from `bd35861` to `c68d684`.
- [Release notes](https://github.com/chipsalliance/synlig/releases)
- [Commits](chipsalliance/synlig@bd35861...c68d684)

---
updated-dependencies:
- dependency-name: third_party/tools/synlig
  dependency-type: direct:production
...

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