Bump third_party/openthread/repo from a0ff14c to afbb2d5 (project-chip#25184)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `a0ff14c` to `afbb2d5`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@a0ff14c...afbb2d5)

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

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Author: dependabot[bot]