submodule: bump third_party/openthread/repo from 36b1b83 to `88cc6c…

…8` (#1915)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `36b1b83` to `88cc6c8`.
- [Commits](openthread/openthread@36b1b83...88cc6c8)

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

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