Bump 3rd_party/ssplit-cpp from 49fde6d to ad2c5a5

Bumps [3rd_party/ssplit-cpp](https://github.com/browsermt/ssplit-cpp) from `49fde6d` to `ad2c5a5`.
- [Release notes](https://github.com/browsermt/ssplit-cpp/releases)
- [Commits](browsermt/ssplit-cpp@49fde6d...ad2c5a5)

---
updated-dependencies:
- dependency-name: 3rd_party/ssplit-cpp
  dependency-type: direct:production
...

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