ci: pin and update some workflow actions

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

This pins the action and download-artifact actions to specific hashes. This also updates audit-check to avoid deprecation issues, and bumps setup-python and rust-toolchain.

Issue

If applicable, what issue does this address?

Closes: #

Testing

If relevant, please state how this was tested. All changes must be tested to work:

Tested most affected actions:

• Audit: run
• Nightly: run
• CI: see checks
• Clear workflow cache: run
• Test docs: see checks
• Codecov: see checks

Checklist

If relevant, ensure the following have been met:

• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (31869de) 28.88% compared to head (2d4f69b) 28.88%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1145   +/-   ##
=======================================
  Coverage   28.88%   28.88%           
=======================================
  Files          95       95           
  Lines       16286    16286           
=======================================
  Hits         4704     4704           
  Misses      11582    11582           

Flag	Coverage Δ
macos-12	30.40% <ø> (ø)
ubuntu-latest	30.32% <ø> (ø)
windows-2019	30.44% <ø> (ø)

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