submodule: bump third_party/openthread/repo from `2ce3d3b` to `78e3b28` (#1456)
submodule: bump third_party/openthread/repo from `2ce3d3b` to `78e3b28` (#1456)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `2ce3d3b` to `78e3b28`.
- [Commits](https://github.com/openthread/openthread/compare/2ce3d3bf0218566484be2e9943b95c755cefebe3...78e3b2812744ededc126c1d12f5d67fdf3ee7f30)

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

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
openthread/ot-br-posix,openthread/borderrouter,openthread/ot-br-posix,openthread/ot-br-posix,openthread/borderrouter,openthread/borderrouter,openthread/borderrouter,openthread/ot-br-posix,openthread/ot-br-posix,openthread/borderrouter,openthread/ot-br-posix,openthread/borderrouter