submodule: bump openthread from 831f2d3 to b2093f4 (#1130)

Bumps [openthread](https://github.com/openthread/openthread) from `831f2d3` to `b2093f4`.
- [Commits](openthread/openthread@831f2d3...b2093f4)

---
updated-dependencies:
- dependency-name: openthread
  dependency-version: b2093f4f9ec0cbd925eeffcc177b0f3669ec46e2
  dependency-type: direct:production
...

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Author: dependabot[bot]