submodules: bump external/sapphire-paratime from 94dd75b to c990d8a

Bumps [external/sapphire-paratime](https://github.com/oasisprotocol/sapphire-paratime) from `94dd75b` to `c990d8a`.
- [Release notes](https://github.com/oasisprotocol/sapphire-paratime/releases)
- [Commits](oasisprotocol/sapphire-paratime@94dd75b...c990d8a)

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

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