submodules: bump external/sapphire-paratime from a13bd49 to 8a9f6b6

Bumps [external/sapphire-paratime](https://github.com/oasisprotocol/sapphire-paratime) from `a13bd49` to `8a9f6b6`.
- [Release notes](https://github.com/oasisprotocol/sapphire-paratime/releases)
- [Commits](oasisprotocol/sapphire-paratime@a13bd49...8a9f6b6)

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

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