Fix update-rust-toolchain workflow

[alexdewar]

Description

The new checkout action (v6) causes problems with the update-rust-toolchain, leading to multiple authentication headers being sent to git, which then fails. Fix by not persisting credentials.

I hacked the workflow to make it run and confirmed that it now works and opens a PR successfully (which I then closed without merging).

Credit goes to the author of update-rust-toolchain for the fix: a-kenji/update-rust-toolchain#75 (comment)

Fixes #1029.

Type of change

• Bug fix (non-breaking change to fix an issue)
• New feature (non-breaking change to add functionality)
• Refactoring (non-breaking, non-functional change to improve maintainability)
• Optimization (non-breaking change to speed up the code)
• Breaking change (whatever its nature)
• Documentation (improve or add documentation)

Key checklist

• All tests pass: $ cargo test
• The documentation builds and looks OK: $ cargo doc

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.45%. Comparing base (db2c40a) to head (6ab6f84).
⚠️ Report is 60 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1037   +/-   ##
=======================================
  Coverage   81.45%   81.45%           
=======================================
  Files          52       52           
  Lines        6497     6497           
  Branches     6497     6497           
=======================================
  Hits         5292     5292           
  Misses        949      949           
  Partials      256      256           

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[Copilot]

Pull request overview

This PR fixes an authentication issue in the update-rust-toolchain GitHub Actions workflow that was introduced by upgrading to actions/checkout@v6. The fix adds persist-credentials: false to prevent multiple authentication headers from being sent, which was causing git operations to fail.

Key Changes:

• Added persist-credentials: false configuration to the checkout step in the update-rust-toolchain workflow

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[dalonsoa]

If it works, it works :)