checkout sources for e2e test

Author: xinsong-cui

.github/workflows/codebuild-ci.yml

@@ -43,6 +43,8 @@ jobs:
     if: github.event_name == 'pull_request' || github.event_name == 'workflow_dispatch'
     runs-on: ubuntu-latest
     steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
       - name: Set start time
         run: echo "WORKFLOW_START_TIME=$(date +%s)" >> $GITHUB_ENV
       - name: Verify PRs are not running malicious code