fix: repair check workflow for external PRs (ethereum#616)

Author: pk910

.github/workflows/per-pr.yml

@@ -72,12 +72,9 @@ jobs:
     steps:
       - name: Checkout Repository
         uses: actions/checkout@v4
-      - name: Extract branch name
-        shell: bash
-        run: echo "branch=${GITHUB_HEAD_REF:-${GITHUB_REF#refs/heads/}}" >> $GITHUB_OUTPUT
-        id: extract_branch
       - name: Kurtosis Assertoor GitHub Action
         uses: ethpandaops/kurtosis-assertoor-github-action@v1
         with:
-          ethereum_package_branch: ${{ steps.extract_branch.outputs.branch }}
+          ethereum_package_url: "."
+          ethereum_package_branch: ""
           ethereum_package_args: .github/tests/mix-assert.yaml