actions-rs is unmaintained

[VictorKoenders]

I noticed that we started getting a lot of warnings in our CI: https://github.com/EspressoSystems/HotShot/actions/runs/3397428731

Annotations
9 warnings
build
Node.js 12 actions are deprecated. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/. Please update the following actions to use Node.js 16: actions-rs/toolchain, Swatinem/rust-cache, Swatinem/rust-cache
build
The `save-state` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
build
The `save-state` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
build
The `save-state` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
build
The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
build
The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
build
The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
build
The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
build
The `set-output` command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

It turns out that action-rs/toolchain is unmaintained: https://github.com/actions-rs/toolchain/issues/216

We have 2 alternatives:

• use https://github.com/dtolnay/rust-toolchain
• Run a script:

    - name: "Install Rust"
      run: |
        rustup toolchain install ${{ inputs.rust }} --profile minimal --no-self-update
        rustup default ${{ inputs.rust }}
      shell: bash

    - uses: Swatinem/rust-cache@v2
      with:
        shared-key: ${{ inputs.cache-key }}

    - name: "Set environment variables used by toolchain"
      run: |
        echo CARGO_TERM_COLOR=always >> $GITHUB_ENV
        echo CARGO_INCREMENTAL=0 >> $GITHUB_ENV
        echo RUST_BACKTRACE=1 >> $GITHUB_ENV
        
        rustc --version --verbose
      shell: bash