Update `shell.nix` to `nixpkgs-24.05` and LLVM 18 (#14651) #12874

	name: macOS CI

	on: [push, pull_request]

	permissions: {}

	concurrency:
	group: ${{ github.workflow }}-${{ github.ref }}
	cancel-in-progress: ${{ github.ref != 'refs/heads/master' }}

	env:
	SPEC_SPLIT_DOTS: 160
	CI_NIX_SHELL: true
	CRYSTAL_OPTS: -Dwithout_iconv

	jobs:
	darwin-test:
	runs-on: ${{ matrix.runs-on }}
	name: ${{ matrix.arch }}
	strategy:
	fail-fast: false
	matrix:
	include:
	- runs-on: macos-13
	arch: x86_64-darwin
	- runs-on: macos-14
	arch: aarch64-darwin

	steps:
	- name: Download Crystal source
	uses: actions/checkout@v4

	- uses: cachix/install-nix-action@v27
	with:
	extra_nix_config: \|
	experimental-features = nix-command

	- uses: cachix/cachix-action@v15
	with:
	name: crystal-ci
	signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'

	- name: Prepare System
	run: bin/ci prepare_system

	- name: Prepare Build
	run: bin/ci prepare_build

	- name: Test
	run: bin/ci build

	- name: Test interpreter
	run: bin/ci with_build_env 'make interpreter_spec'

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