submodule: bump third_party/openthread/repo from 9842f4b to beeef5f (openthread#3126)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `9842f4b` to `beeef5f`.
- [Commits](openthread/openthread@9842f4b...beeef5f)

---
updated-dependencies:
- dependency-name: third_party/openthread/repo
  dependency-version: beeef5f8a699b5bf5e9f1cef89fff99792abc803
  dependency-type: direct:production
...

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

Author: dependabot[bot]