Checkout repo in preconditions job

Author: atextor

.github/workflows/release-workflow.yml

@@ -10,6 +10,9 @@ jobs:
     name: Check preconditions
     runs-on: ubuntu-20.04
     steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
       # Required for Maven
       - name: Set up JDK 17
         uses: actions/setup-java@v2