submodule: bump openthread from 19dc5ce to ade9c2b

Bumps [openthread](https://github.com/openthread/openthread) from `19dc5ce` to `ade9c2b`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@19dc5ce...ade9c2b)

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

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