Bump third_party/openthread/repo from 2aeb8b8 to 6e46e2e

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `2aeb8b8` to `6e46e2e`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@2aeb8b8...6e46e2e)

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

Signed-off-by: dependabot[bot] <[email protected]>