submodule: bump openthread from b0e7b14 to 2bc7712

Bumps [openthread](https://github.com/openthread/openthread) from `b0e7b14` to `2bc7712`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@b0e7b14...2bc7712)

---
updated-dependencies:
- dependency-name: openthread
  dependency-version: 2bc7712f57af22058770d1ef131ad3da79a0c764
  dependency-type: direct:production
...

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Author: dependabot[bot]