Bump third_party/yosys from a2f59cf to d21c464

Bumps [third_party/yosys](https://github.com/YosysHQ/yosys) from `a2f59cf` to `d21c464`.
- [Release notes](https://github.com/YosysHQ/yosys/releases)
- [Commits](YosysHQ/yosys@a2f59cf...d21c464)

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

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