Bump third_party/ot-br-posix/repo from 03132d3 to 8df5dc3

Bumps [third_party/ot-br-posix/repo](https://github.com/openthread/ot-br-posix) from `03132d3` to `8df5dc3`.
- [Release notes](https://github.com/openthread/ot-br-posix/releases)
- [Commits](openthread/ot-br-posix@03132d3...8df5dc3)

---
updated-dependencies:
- dependency-name: third_party/ot-br-posix/repo
  dependency-type: direct:production
...

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