add checkout before reusable workflow

.github/workflows/2023-PyData_Berlin-python-pdf-workflow.yaml

@@ -27,7 +27,7 @@ jobs:
     steps:
     - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
       if: github.ref == 'refs/heads/main'  # Only checkout when the branch is 'main'
-    - name: Check for backend file changes
+    - name: Check for 2023_PyData_Berlin file changes
       uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36 #v3.0.2
       id: filter
       with:
@@ -43,6 +43,7 @@ jobs:
     needs: changes
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
       - name: Trigger Reusable Workflow
         uses: ./.github/workflows/lint_python_reusable.yaml
         with: