use ref commit

Author: radofuchs

.github/workflows/e2e_tests.yaml

@@ -18,9 +18,8 @@ jobs:
 
           # On PR_TARGET → the PR head *commit* (reproducible).
           # On push      → the pushed commit that triggered the workflow.
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.ref || github.sha }}
 
-          fetch-depth: 0
           # Don’t keep credentials when running untrusted PR code under PR_TARGET.
           persist-credentials: ${{ github.event_name != 'pull_request_target' }}