submodule: bump openthread from f0cb5a3 to 262b998 (#816)

Bumps [openthread](https://github.com/openthread/openthread) from `f0cb5a3` to `262b998`.
- [Commits](openthread/openthread@f0cb5a3...262b998)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>