submodule: bump openthread from f0cb5a3 to b8d2e5d

Bumps [openthread](https://github.com/openthread/openthread) from `f0cb5a3` to `b8d2e5d`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@f0cb5a3...b8d2e5d)

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

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