mysql backend creates queries using CONVERT_TZ even when this is not supported

[Klaas van Schelven]

To test whether a mysql server has the zoninfo database loaded (feature name: has_zoneinfo_database), the [following code](​https://github.com/django/django/blob/1fe0b167af3611cca79e8a8092ee929312193c6f/django/db/backends/mysql/base.py#L410) is run:

CONVERT_TZ('2001-01-01 01:00:00', 'UTC', 'UTC') IS NOT NULL

However, this test is not actually used (i.e. there is no condition on the feature being True) when [generating sql](​https://github.com/django/django/blob/main/django/db/backends/mysql/operations.py#L94), despite the fact that the generated sql contains something that we know will evaluate to NULL

This shows up when filtering like so:

Foo.objects(some_datetimefield__date="2023-06-16")

which evaluates to the empty queryset, despite there being such objects. USE_TZ = True, obviously