Query optimization in YearLookup breaks filtering by "__iso_year"

[Florian Demmer]

The optimization to use BETWEEN instead of the EXTRACT operation in ​YearLookup is also registered for the ​"__iso_year" lookup, which breaks the functionality provided by ​ExtractIsoYear when used via the lookup.

This has unfortunately been broken ever since ExtractIsoYear was introduced in Django 2.2 via #28649 and wasn't easy to track down since ExtractIsoYear when used by itself eg. in an annotation works perfectly fine. Just when using the lookup in a filter, the optimization is used (even when explicitly using an annotation):

# annotation works
>>> qs = DTModel.objects.annotate(extracted=ExtractIsoYear('start_date')).only('id')
>>> print(qs.query)
SELECT "db_functions_dtmodel"."id", EXTRACT('isoyear' FROM "db_functions_dtmodel"."start_date") AS "extracted" FROM "db_functions_dtmodel"

# explicit annotation used in filter does not use "extracted" and adds BETWEEN
>>> print(qs.filter(extracted=2020).query)
SELECT "db_functions_dtmodel"."id", EXTRACT('isoyear' FROM "db_functions_dtmodel"."start_date") AS "extracted" FROM "db_functions_dtmodel" WHERE "db_functions_dtmodel"."start_date" BETWEEN 2020-01-01 AND 2020-12-31

# implicit lookup uses BETWEEN
print(DTModel.objects.filter(start_date__iso_year=2020).only('id').query)
SELECT "db_functions_dtmodel"."id" FROM "db_functions_dtmodel" WHERE "db_functions_dtmodel"."start_date" BETWEEN 2020-01-01 AND 2020-12-31

This results in the wrong data being returned by filters using iso_year.

This PR fixes the behaviour, reverts the invalid changes to the tests and extends one test to catch this problem: ​https://github.com/django/django/pull/14157