pin to nb_helpers

.github/workflows/cleanup.yml

@@ -19,7 +19,7 @@ jobs:
             python-version: 3.11
         - name: Install Dependencies
           run: |
-            python -m pip install -r requirements.txt
+            python -m pip install nb_helpers
         - name: Test clean up .ipynb files
           shell: bash
           run: |