Replace unmaintained actions-rs/toolchain action in CI workflows

[striezel]

Basically all of the actions-rs/* actions are unmaintained. See https://github.com/actions-rs/toolchain/issues/216 for more information. Due to their age they generate several warnings in CI runs.

To get rid of those warnings the occurrences of actions-rs/toolchain are replaced by dtolnay/rust-toolchain.

Fixes #17.

[tarcieri]

Hmm, we started getting build failures and I think this might be related:

https://github.com/RustCrypto/password-hashes/actions/runs/4331611849/jobs/7563556788

Run cargo build --benches
error: failed to get `base64ct` as a dependency of package `argon2 v0.5.0-pre.0 (/home/runner/work/password-hashes/password-hashes/argon2)`

Caused by:
  failed to load source for dependency `base64ct`

Caused by:
  Unable to update registry `crates-io`

Caused by:
  usage of sparse registries requires `-Z sparse-registry`
Error: Process completed with exit code [1](https://github.com/RustCrypto/password-hashes/actions/runs/4331611849/jobs/7563556788#step:6:1)01.

Going to try reverting and see if it helps

[tarcieri]

That seems to have fixed it. Not sure what the problem is?

[tarcieri]

Hmm, something seems to be setting the CARGO_REGISTRIES_CRATES_IO_PROTOCOL environment variable:

https://github.com/RustCrypto/password-hashes/actions/runs/4331611849/jobs/7564040182

  cargo build --benches
  shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
  env:
    CARGO_INCREMENTAL: 0
    CARGO_TERM_COLOR: always
    CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse

Maybe pinning to a newer nightly would resolve the issue?

[striezel]

Hmm, something seems to be setting the CARGO_REGISTRIES_CRATES_IO_PROTOCOL environment variable:

https://github.com/RustCrypto/password-hashes/actions/runs/4331611849/jobs/7564040182

Yes. Looking at https://github.com/RustCrypto/password-hashes/actions/runs/4331611849/jobs/7563556788, this seems to be done by dtolnay/rust-toolchain for certain versions of Rust:

Run : enable Cargo sparse registry
  : enable Cargo sparse registry
  # except on 1.66 and 1.67, on which it is unstable
  if [ -z "${CARGO_REGISTRIES_CRATES_IO_PROTOCOL+set}" -o -f "/home/runner/work/_temp"/.implicit_cargo_registries_crates_io_protocol ]; then
    touch "/home/runner/work/_temp"/.implicit_cargo_registries_crates_io_protocol || true
    if rustc +nightly-2022-12-25 --version --verbose | (! grep -q '^release: 1\.6[67]\.'); then
      echo CARGO_REGISTRIES_CRATES_IO_PROTOCOL=sparse >> $GITHUB_ENV
    else
      echo CARGO_REGISTRIES_CRATES_IO_PROTOCOL=git >> $GITHUB_ENV
    fi
  fi

I am not sure what's the reason for this behaviour.