submodule: bump third_party/openthread/repo from 1d81283 to `6bfe59…

…d` (#2069)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `1d81283` to `6bfe59d`.
- [Commits](openthread/openthread@1d81283...6bfe59d)

---
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>