submodule: bump third_party/openthread/repo from `c8902e9` to `8a0e7b8` (#814)
submodule: bump third_party/openthread/repo from `c8902e9` to `8a0e7b8` (#814)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `c8902e9` to `8a0e7b8`.
- [Commits](https://github.com/openthread/openthread/compare/c8902e9419a17e618cec5827391ac2f3cc0b7b1e...8a0e7b8c4e02f0b5cc058b69b14c2261db9c1cea)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
openthread/borderrouter,openthread/ot-br-posix,openthread/ot-br-posix,openthread/ot-br-posix,openthread/ot-br-posix,openthread/borderrouter,openthread/borderrouter,openthread/borderrouter,openthread/borderrouter,openthread/borderrouter,openthread/ot-br-posix,openthread/ot-br-posix