[FIX] awesome_owl: include missing bundle

Author: fdardenne

awesome_owl/__manifest__.py

@@ -29,6 +29,7 @@
     'assets': {
         'awesome_owl.assets_playground': [
             ('include', 'web._assets_helpers'),
+            ('include', 'web._assets_backend_helpers'),
             'web/static/src/scss/pre_variables.scss',
             'web/static/lib/bootstrap/scss/_variables.scss',
             ('include', 'web._assets_bootstrap'),