submodule: bump openthread from 9f6921c to 944a246

Bumps [openthread](https://github.com/openthread/openthread) from `9f6921c` to `944a246`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@9f6921c...944a246)

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

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