bump actions/checkout from 2.4.0 to 3.0.2 (via #94)

Author: dependabot[bot]

.github/workflows/build.yml

@@ -28,7 +28,7 @@ jobs:
           - "--prefer-lowest"
     steps:
       - name: Checkout
-        uses: actions/checkout@v2.4.0
+        uses: actions/checkout@v3.0.2
 
       - name: Validate composer.json and composer.lock
         run: composer validate