Update workflow version

Author: gdonald

.github/workflows/raku.yml

@@ -6,7 +6,7 @@ jobs:
     name: Tests
     steps:
     - name: Checkout
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
     - name: Runs tests
       id: tests
       uses: JJ/raku-container-action@master