Bump third_party/ot-br-posix/repo from bd15f71 to b852388

Bumps [third_party/ot-br-posix/repo](https://github.com/openthread/ot-br-posix) from `bd15f71` to `b852388`.
- [Release notes](https://github.com/openthread/ot-br-posix/releases)
- [Commits](openthread/ot-br-posix@bd15f71...b852388)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

third_party/ot-br-posix/repo

@@ -0,0 +1 @@
+b8523883c4692c653f008596873d09bb69669bab