submodule: bump openthread from 74573b5 to 1fceb22 (#859)

Bumps [openthread](https://github.com/openthread/openthread) from `74573b5` to `1fceb22`.
- [Commits](openthread/openthread@74573b5...1fceb22)

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

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