submodule: bump openthread from b4282a8 to e4479fb

Bumps [openthread](https://github.com/openthread/openthread) from `b4282a8` to `e4479fb`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@b4282a8...e4479fb)

---
updated-dependencies:
- dependency-name: openthread
  dependency-version: e4479fb6b1f6df883e2a06520c3d13db75f331d6
  dependency-type: direct:production
...

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Author: dependabot[bot]