Tidy up the macos runner list

[grahamc]

Description

Checklist

• Tested changes against a test repository
• Added or updated relevant documentation (leave unchecked if not applicable)
• (If this PR is for a release) Updated README to point to the new tag (leave unchecked if not applicable)

Summary by CodeRabbit

• Chores
  • Updated CI/CD infrastructure by replacing specific macOS runner versions with the latest ARM64 variant, streamlining the build matrix configuration.
  • Simplified workflow execution logic to ensure consistent step execution across all test runners.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Removed specific macOS runners (macos-13-large, macos-14-large, macos-14-xlarge) from the CI matrix and replaced them with macos-latest (arm64). Simplified the conditional logic by removing the guard clause that excluded certain macOS runners from the "Render the devshell" step, allowing it to run unconditionally on all matrix runners.

Changes

Cohort / File(s)	Summary
CI Workflow Configuration \.github/workflows/ci\.yml	Updated macOS runner selection in install-nix matrix; removed conditional exclusion of specific macOS runners from devshell rendering step, now runs unconditionally across all matrix targets.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• Drop x86_64-darwin #207: Modifies the same .github/workflows/ci.yml file's macOS runner matrix and devshell step conditional handling, managing guards for specific macOS runners.

Suggested reviewers

• colemickels
• cole-h

Poem

🐰 macOS runners hopped away,
Arm64 takes the stage today,
Conditionals removed with glee,
The devshell runs wild and free!
Simplicity's the rabbit's way! 🚀

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Tidy up the macos runner list' directly and clearly describes the main change: simplifying and reorganizing the macOS runners configuration in the CI workflow.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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