Ensure correct Swift version is set

Author: lordcodes

.github/workflows/swift.yml

@@ -20,6 +20,11 @@ jobs:
         restore-keys: |
           ${{ runner.os }}-spm-
 
+    - name: Setup Swift
+      uses: swift-actions/setup-swift@v1
+      with:
+        swift-version: "5.6"
+
     - name: Build
       run: swift build -v