build(deps): bump third_party/cctz from c8cd07c to b6d7a85

Bumps [third_party/cctz](https://github.com/google/cctz) from `c8cd07c` to `b6d7a85`.
- [Release notes](https://github.com/google/cctz/releases)
- [Commits](google/cctz@c8cd07c...b6d7a85)

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

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