submodules: bump external/oasis-sdk from 385af35 to de6715a

Bumps [external/oasis-sdk](https://github.com/oasisprotocol/oasis-sdk) from `385af35` to `de6715a`.
- [Commits](oasisprotocol/oasis-sdk@385af35...de6715a)

---
updated-dependencies:
- dependency-name: external/oasis-sdk
  dependency-type: direct:production
...

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