submodule: bump third_party/openthread/repo from `b42261f` to `3a90ed8` (#973)
submodule: bump third_party/openthread/repo from `b42261f` to `3a90ed8` (#973)

Bumps [third_party/openthread/repo](https://github.com/openthread/openthread) from `b42261f` to `3a90ed8`.
- [Commits](https://github.com/openthread/openthread/compare/b42261f88c6c8360cb8738118c0767f886d76110...3a90ed81f0a00761510630162b59f81446df995b)

---
updated-dependencies:
- dependency-name: third_party/openthread/repo
  dependency-type: direct:production
...

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

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