GHA: Use latest Xcode

... and checkout v4.

Author: helje5

.github/workflows/swift.yml

@@ -13,9 +13,9 @@ jobs:
       - name: Select latest available Xcode
         uses: maxim-lobanov/[email protected]
         with:
-          xcode-version: 12.2
+          xcode-version: latest
       - name: Checkout Repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
       - name: Build Swift Debug Package
         run: swift build -c debug
       - name: Build Swift Release Package