submodule: bump openthread from a05954b to 6edb06e

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

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

Signed-off-by: dependabot[bot] <[email protected]>