Bump third_party/ot-br-posix/repo from `f6a0a81` to `8299da3` (#28918)

Bumps [third_party/ot-br-posix/repo](https://github.com/openthread/ot-br-posix) from `f6a0a81` to `8299da3`.
- [Release notes](https://github.com/openthread/ot-br-posix/releases)
- [Commits](https://github.com/openthread/ot-br-posix/compare/f6a0a81d104124f421ceab640e3787611b9f667b...8299da302aebf807e76885e9f758df18100522d1)

---
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 f6a0a81..8299da3 160000
--- a/third_party/ot-br-posix/repo
+++ b/third_party/ot-br-posix/repo
@@ -1 +1 @@
-Subproject commit f6a0a81d104124f421ceab640e3787611b9f667b
+Subproject commit 8299da302aebf807e76885e9f758df18100522d1