Update stale test module cross-reference in a docstring

test_bibliotheca_importer.py was renamed to
tests/manager/integration/license/bibliotheca/test_importer.py, so point
the docstring at the new location. Use the full path rather than the bare
module name, since boundless/ and overdrive/ each have a test_importer.py
of their own.

Author: jonathangreen

tests/manager/celery/tasks/test_bibliotheca.py

@@ -413,7 +413,8 @@ def test_events_processed_end_to_end(
         redis_fixture: RedisFixture,
     ) -> None:
         """Smoke test: the full Celery task path processes an event and advances the
-        Timestamp.  Detailed event-handling assertions live in test_bibliotheca_importer.
+        Timestamp.  Detailed event-handling assertions live in
+        tests/manager/integration/license/bibliotheca/test_importer.py.
         """
         collection = bibliotheca_task_fixture.collection