Bump chisel3 from `5b13d04b` to `721adc5c` (#351)

Bumps [chisel3](https://github.com/freechipsproject/chisel3) from `5b13d04b` to `721adc5c`.
- [Release notes](https://github.com/freechipsproject/chisel3/releases)
- [Commits](https://github.com/freechipsproject/chisel3/compare/5b13d04b28ddd05e4acbc5b9b3755c92ac0d9515...721adc5c5509af48118afae44afa6b8a0107a926

)

---
updated-dependencies:
- dependency-name: chisel3
  dependency-type: direct:production
...

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