[infra] Fix OneCollector Dangerous-Workflow (#3227)

Author: Kielek

.github/workflows/ci-Exporter.OneCollector-Integration.yml

@@ -38,7 +38,7 @@ jobs:
     steps:
     - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
       with:
-        ref: ${{ github.event.pull_request.head.sha || github.ref }} # Run on the fork branch once approved
+        ref: refs/pull/${{ github.event.pull_request.number }}/merge # Run on the merge commit once approved
 
     - name: Setup dotnet
       uses: actions/setup-dotnet@d4c94342e560b34958eacfc5d055d21461ed1c5d # v5.0.0