submodule: bump openthread from `15a9c4c` to `dd4ce78` (#35)
submodule: bump openthread from `15a9c4c` to `dd4ce78` (#35)

Bumps [openthread](https://github.com/openthread/openthread) from `15a9c4c` to `dd4ce78`.
- [Commits](https://github.com/openthread/openthread/compare/15a9c4c0bd5cbd5dd9abba87b1c4a5b43ad61b37...dd4ce786a8fa67c66265408a923535f4b5e980f6)

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

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

Co-authored-by: dependabot[bot] <1c358da00a777d4e9898c1280ab801e2df165188@users.noreply.github.com>
openthread/ot-ifx,Infineon/ot-ifx-release,openthread/ot-ifx,Infineon/ot-ifx-release,openthread/ot-ifx,Infineon/ot-ifx-release