Updated workflow to use latest Xcode

Author: d-exclaimation

Diff for: .github/workflows/test.yml

@@ -28,6 +28,8 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: maxim-lobanov/setup-xcode@v1
+        with:
+          xcode-version: latest-stable
       - name: Build
         run: swift build
       - name: Run tests