Bump third_party/ot-br-posix/repo from `8299da3` to `8a280e3` (#29148)

Bumps [third_party/ot-br-posix/repo](https://github.com/openthread/ot-br-posix) from `8299da3` to `8a280e3`.
- [Release notes](https://github.com/openthread/ot-br-posix/releases)
- [Commits](https://github.com/openthread/ot-br-posix/compare/8299da302aebf807e76885e9f758df18100522d1...8a280e3516641f707324bbc83059736d02f68955)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
diff --git a/third_party/ot-br-posix/repo b/third_party/ot-br-posix/repo
index 8299da3..8a280e3 160000
--- a/third_party/ot-br-posix/repo
+++ b/third_party/ot-br-posix/repo
@@ -1 +1 @@
-Subproject commit 8299da302aebf807e76885e9f758df18100522d1
+Subproject commit 8a280e3516641f707324bbc83059736d02f68955