Bump third_party/openthread/repo from 2aeb8b8 to 287dbfa (#36012)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `2aeb8b8` to `287dbfa`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@2aeb8b8...287dbfa)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Andrei Litvin <[email protected]>