Address non-serializable task results deprecation warnings

The issue includes reference to deprecation warnings of legacy STORAGES
configuration key and of the use of project.license TOML table, but
there is no reference in the codebase or in the CI configuration of
the deprecated storage keys and the pyproject.toml doesnt' contain the
referenced license table.

The non-use of any license table is consistent with other component's
pyproject.py files (e.g, pulpcore and pulp_rpm). This is curious, as
I would expect a license field/table in the pyproject for all Pulp
components.

Closes #354

Author: pedro-psb

CHANGES/354.bugfix

@@ -0,0 +1 @@
+Addressed the deprecation warning of non-serializable task results.

pulp_npm/app/tasks/synchronizing.py

@@ -43,7 +43,7 @@ def synchronize(remote_pk, repository_pk, mirror=False):
     first_stage = NpmFirstStage(remote, deferred_download)
     repover = DeclarativeVersion(first_stage, repository, mirror=mirror).create()
     repover_serialized = RepositoryVersionSerializer(instance=repover, context={"request": None})
-    return repover_serialized
+    return repover_serialized.data
 
 
 class NpmFirstStage(Stage):