Try and fix GitHub Actions

Author: amayers

.github/workflows/swift.yml

@@ -14,10 +14,8 @@ jobs:
     steps:
     - uses: actions/checkout@v2
 
-    - name: Switch to Xcode 12.0
-      uses: maxim-lobanov/setup-xcode@1.0
-      with:
-        xcode-version: 12.0
+    - name: Switch to latest Xcode
+      uses: maxim-lobanov/setup-xcode@v1.2.1
     - name: Build
       run: swift build -v
     - name: Run tests