Update CI-master_tests.yml

.github/workflows/CI-master_tests.yml

@@ -120,11 +120,9 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - name: Checkout
-        uses: actions/checkout@master
+      - uses: actions/checkout@master
         with:
-          persist-credentials: false
-          fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.ref }}
 
       - name: Build linpeas
         run: |