Bump tests/third_party/yosys from 81df855 to b2d7858

Bumps [tests/third_party/yosys](https://github.com/YosysHQ/yosys) from `81df855` to `b2d7858`.
- [Release notes](https://github.com/YosysHQ/yosys/releases)
- [Commits](YosysHQ/yosys@81df855...b2d7858)

---
updated-dependencies:
- dependency-name: tests/third_party/yosys
  dependency-type: direct:production
...

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