CI: github: openssl-master.yml misses actions/checkout

The job can't run setup-vtest because the actions/checkout use line is
missing.

.github/workflows/openssl-master.yml

@@ -13,6 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     if: ${{ github.repository_owner == 'haproxy' || github.event_name == 'workflow_dispatch' }}
     steps:
+      - uses: actions/checkout@v5
       - name: Install apt dependencies
         run: |
           sudo apt-get update -o Acquire::Languages=none -o Acquire::Translation=none