submodule: bump openthread from a05954b to 6edb06e (#723)

Bumps [openthread](https://github.com/openthread/openthread) from `a05954b` to `6edb06e`.
- [Commits](openthread/openthread@a05954b...6edb06e)

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

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