Update actions/checkout to v3

Author: Maria Shodunke

.github/workflows/build.yml

@@ -37,7 +37,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Set up Java
         uses: actions/setup-java@v1