Bump third_party/ot-br-posix/repo from c5a7a35 to 9bdaa91

Bumps [third_party/ot-br-posix/repo](https://github.com/openthread/ot-br-posix) from `c5a7a35` to `9bdaa91`.
- [Release notes](https://github.com/openthread/ot-br-posix/releases)
- [Commits](openthread/ot-br-posix@c5a7a35...9bdaa91)

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

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