Bump third_party/openthread/repo from 2aeb8b8 to 7ec2c31

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `2aeb8b8` to `7ec2c31`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@2aeb8b8...7ec2c31)

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

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