Bump third_party/ot-br-posix/repo from 28b5c48 to 7aa6689 (project-chip#41994)

Bumps [third_party/ot-br-posix/repo](https://github.com/openthread/ot-br-posix) from `28b5c48` to `7aa6689`.
- [Release notes](https://github.com/openthread/ot-br-posix/releases)
- [Commits](openthread/ot-br-posix@28b5c48...7aa6689)

---
updated-dependencies:
- dependency-name: third_party/ot-br-posix/repo
  dependency-version: 7aa66892f185a963d4dc84fe4d769b333bfeb247
  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]>

Author: dependabot[bot]