Bump lib/CPP_BIDS from ad68d19 to 31606c3

Bumps [lib/CPP_BIDS](https://github.com/cpp-lln-lab/CPP_BIDS) from `ad68d19` to `31606c3`.
- [Release notes](https://github.com/cpp-lln-lab/CPP_BIDS/releases)
- [Commits](cpp-lln-lab/CPP_BIDS@ad68d19...31606c3)

---
updated-dependencies:
- dependency-name: lib/CPP_BIDS
  dependency-type: direct:production
...

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

Author: dependabot[bot]