GitHub Actions: Add Checkout action

.github/workflows/test.yml

@@ -4,6 +4,10 @@ jobs:
   Syntax-Check:
     runs-on: ubuntu-latest
     steps:
+        # Checkout the git repo
+      - name: Checkout
+        uses: actions/checkout@v2
+        
       - name: Install Dependencies
         run: sudo apt-get install lua5.1
         
@@ -20,6 +24,10 @@ jobs:
   Busted:
     runs-on: ubuntu-latest
     steps:
+        # Checkout the git repo
+      - name: Checkout
+        uses: actions/checkout@v2
+        
       - name: Install Dependencies
         run: sudo apt-get install lua5.1 luarocks