submodules: bump external/sapphire-paratime from 0a61d8c to 7840c23

Bumps [external/sapphire-paratime](https://github.com/oasisprotocol/sapphire-paratime) from `0a61d8c` to `7840c23`.
- [Release notes](https://github.com/oasisprotocol/sapphire-paratime/releases)
- [Commits](oasisprotocol/sapphire-paratime@0a61d8c...7840c23)

---
updated-dependencies:
- dependency-name: external/sapphire-paratime
  dependency-version: 7840c239673b9ef8b8b249fe92bc64e431603564
  dependency-type: direct:production
...

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

Author: dependabot[bot]