build(deps): bump third_party/prjxray from a1f3ae2 to 731fbce (#3841

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Bumps [third_party/prjxray](https://github.com/f4pga/prjxray) from `a1f3ae2` to `731fbce`.
- [Commits](f4pga/prjxray@a1f3ae2...731fbce)

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

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