Update unittest.yaml

Author: pan-x-c

.github/workflows/unittest.yaml

@@ -16,9 +16,10 @@ jobs:
     runs-on: self-hosted
 
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v4
       with:
         path: trinity-${{ github.run_id }}
+        ref: refs/pull/${{ github.event.issue.number }}/head
 
     - name: Setup docker compose
       working-directory: trinity-${{ github.run_id }}/.github/workflows/docker