GHA: Build against Xcode latest

...

Author: helje5

.github/workflows/swift.yml

@@ -11,9 +11,9 @@ jobs:
     runs-on: macos-latest
     steps:
       - name: Select latest available Xcode
-        uses: maxim-lobanov/setup-xcode@v1.2.1
+        uses: maxim-lobanov/setup-xcode@v1.5.1
         with:
-          xcode-version: 12.2
+          xcode-version: latest
       - name: Checkout Repository
         uses: actions/checkout@v2
       - name: Build Swift Debug Package