ci: Checkout pull request ref instead

Commit 1780630 set the pull request event to `pull_request_target`, which means the pipelines run on the base ref with the secrets from base as well. That's all fine, but we actually want to test the code on the pull request ref

.github/workflows/test.yaml

@@ -12,6 +12,8 @@ jobs:
     steps:
       - name: Checkout hypernode-deploy
         uses: actions/checkout@v3
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
       - name: Run general testsuite
         if: ${{ matrix.testsuite == 'general' }}
         run: MAGENTO_REPO=./magento2 ./runtests.sh general