submodule: bump openthread from 213665c to 262b998

Bumps [openthread](https://github.com/openthread/openthread) from `213665c` to `262b998`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@213665c...262b998)

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

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