Update checkout action to v2

Author: fmbenhassine

.github/workflows/release.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - name: Checkout source code
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
         with:
           ref: master
       - name: Set up JDK 11