Bump rustversion from 1.0.19 to 1.0.20 (#711)

Bumps [rustversion](https://github.com/dtolnay/rustversion) from 1.0.19 to 1.0.20.
- [Release notes](https://github.com/dtolnay/rustversion/releases)
- [Commits](dtolnay/rustversion@1.0.19...1.0.20)

---
updated-dependencies:
- dependency-name: rustversion
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]