submodule: bump openthread from 3a28b7b to 09698fa

Bumps [openthread](https://github.com/openthread/openthread) from `3a28b7b` to `09698fa`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@3a28b7b...09698fa)

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

Signed-off-by: dependabot[bot] <support@github.com>