submodule: bump openthread from 61d9e72 to c5b4cd7 (#358)

Bumps [openthread](https://github.com/openthread/openthread) from `61d9e72` to `c5b4cd7`.
- [Commits](openthread/openthread@61d9e72...c5b4cd7)

---
updated-dependencies:
- dependency-name: openthread
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>