submodule: bump third_party/openthread/repo from d015004 to `b42be4…

…c` (#2512)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `d015004` to `b42be4c`.
- [Commits](openthread/openthread@d015004...b42be4c)

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

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