Prevent RuntimeWarnings about naive datetimes

[adamchainz]

Running all benchmarks locally with asv’s --show-stderr option, I saw the below warning repeated many times from query_benchmarks.queryset_filter_chain.benchmark.FilterChain.time_filter_chain:

  warnings.warn(
/.../python3.12/site-packages/django/db/models/fields/__init__.py:1669: RuntimeWarning: DateTimeField Book.date_published received a naive datetime (2024-02-23 15:00:07.507742) while time zone support is active.

It was repeated for both date_created and date_published.

This should be fixed to avoid the possible output spam and ensure the benchmark simulates a typical situation.