Update checkout action version in build workflow

Updated checkout action version from v2 to v3

Author: karianna

.github/workflows/build.yml

@@ -15,7 +15,7 @@ jobs:
         jdk: ['11']
         os: [ubuntu-latest]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Set up JDK ${{ matrix.jdk }}
       uses: actions/setup-java@v1
       with: