Support multi toolchain like `stable, nightly`?

[jmjoy]

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• [x] Is this related to the actions-rs Actions? If you think it's a problem related to Github Actions in general, use GitHub Community forum instead: https://github.community
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Motivation

Like components, which can specify multi item split by ,, it should be better to also support multi toolchain. In my scene, I often use cargo build in stable toolchain, and then use cargo +nighlty fmt in nightly toolchain, which need both toolchain installed.

Workflow example

      - name: Install Rust Stable
        uses: actions-rs/toolchain@v1
        with:
          toolchain: stable, nightly
          override: true
          components: rustfmt```