Drop "regenerate manifest" GHA step

Author: tcompa

.github/workflows/build_and_test.yml

@@ -42,9 +42,6 @@ jobs:
       - name: Install some testing dependencies (hard-coded)
         run: python -m pip install pytest pytest-cov devtools jsonschema requests wget pooch
 
-      - name: Regenerate the manifest
-        run: python src/fractal_helper_tasks/dev/create_manifest.py
-
       - name: Cache Pooch folder
         id: cache-pooch-folder
         uses: actions/cache@v3