submodule: bump third_party/openthread/repo from b200c96 to `7c5dca…

…1` (#1871)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `b200c96` to `7c5dca1`.
- [Commits](openthread/openthread@b200c96...7c5dca1)

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

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