Bump chisel3 from 818cb70 to 1247147 (#433)

Bumps [chisel3](https://github.com/chipsalliance/chisel3) from `818cb70` to `1247147`.
- [Release notes](https://github.com/chipsalliance/chisel3/releases)
- [Commits](chipsalliance/chisel@818cb70...1247147)

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

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