Chore(deps): Bump dtolnay/rust-toolchain in /.github/actions/setup-rust (#1904)

Bumps [dtolnay/rust-toolchain](https://github.com/dtolnay/rust-toolchain) from 2c7215f132e9ebf062739d9130488b56d53c060c to 6c977a6ca4077a0ceb28ffbe03f59d46e9ac8772.
- [Release notes](https://github.com/dtolnay/rust-toolchain/releases)
- [Commits](https://github.com/dtolnay/rust-toolchain/compare/2c7215f132e9ebf062739d9130488b56d53c060c...6c977a6ca4077a0ceb28ffbe03f59d46e9ac8772)

---
updated-dependencies:
- dependency-name: dtolnay/rust-toolchain
  dependency-version: 6c977a6ca4077a0ceb28ffbe03f59d46e9ac8772
  dependency-type: direct:production
...

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