submodule: bump openthread from 74061ee to 3b30c84

Bumps [openthread](https://github.com/openthread/openthread) from `74061ee` to `3b30c84`.
- [Release notes](https://github.com/openthread/openthread/releases)
- [Commits](openthread/openthread@74061ee...3b30c84)

---
updated-dependencies:
- dependency-name: openthread
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>