submodule: bump openthread from b92bd46 to dc4acf0

Bumps [openthread](https://github.com/openthread/openthread) from `b92bd46` to `dc4acf0`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@b92bd46...dc4acf0)

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

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