Upgrade GitHub Action checkout

https://github.com/actions/checkout/releases

Author: cclauss

.github/workflows/macOS-tests.yml

@@ -33,7 +33,7 @@ jobs:
       group: spm-${{ github.run_id }}
       cancel-in-progress: false
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Resolve dependencies
         run: swift package resolve
       - name: Build