Set github actions version

Author: luizmb

.github/workflows/swift.yml

@@ -8,8 +8,18 @@ on:
 
 jobs:
   build:
-    runs-on: macos-11
+    name: Swift on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        swift: ["5.7"]
     steps:
+    - uses: swift-actions/setup-swift@v1
+      with:
+        swift-version: ${{ matrix.swift }}
+    - name: Get swift version
+      run: swift --version
     - name: Cache Mint
       uses: actions/cache@v2
       with: