Ensure repo is checked out before running validate issue action (#37972)

Author: ijjk

.github/workflows/validate_issue.yml

@@ -7,6 +7,7 @@ jobs:
   validate:
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/checkout@v3
       - uses: ./.github/issue-validator
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}