ci: drop x64 arch pin from CI matrix (#117)

macos-latest now resolves to an arm64-only image, and pinning arch: x64 makes setup-julia fail there. arch never actually varied across this matrix, so just drop it and let setup-julia pick the right one per runner.

Co-authored-by: Claude <noreply@anthropic.com>

Author: sethaxen

.github/workflows/CI.yml

@@ -16,7 +16,7 @@ concurrency:
 
 jobs:
   test:
-    name: ${{ matrix.downgrade && 'Downgrade / ' || '' }}Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }}
+    name: ${{ matrix.downgrade && 'Downgrade / ' || '' }}Julia ${{ matrix.version }} - ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -28,29 +28,23 @@ jobs:
           - 'pre'
         os:
           - ubuntu-latest
-        arch:
-          - x64
         downgrade: [false]
         include:
           - version: '1'
             os: windows-latest
-            arch: x64
             downgrade: false
           - version: '1'
             os: macOS-latest
-            arch: x64
             downgrade: false
           - version: 'min'
             os: ubuntu-latest
-            arch: x64
             downgrade: true
     steps:
       - uses: actions/checkout@v7
       - uses: julia-actions/setup-julia@v3
         id: setup-julia
         with:
           version: ${{ matrix.version }}
-          arch: ${{ matrix.arch }}
       - uses: julia-actions/cache@v3
       - uses: julia-actions/julia-downgrade-compat@v2
         with: