Use the overridable get_default_farm when starting S3 imports

Closes #1727 (closed)

Fixing the expected failures on starting processes with farms could have allowed us to catch this. I added some new tests with mocks to check that the correct get_default_farm is called, and opened https://redmine.teklia.com/issues/7025 to deal with all the other expected failures.

arkindex/process/serializers/imports.py

@@ -18,6 +18,7 @@ from arkindex.process.models import (
     WorkerRun,
     WorkerVersionState,
 )
+from arkindex.process.utils import get_default_farm
 from arkindex.project.mixins import ProcessACLMixin
 from arkindex.project.serializer_fields import EnumField, LinearRingField
 from arkindex.project.validators import MaxValueValidator
@@ -26,7 +27,6 @@ from arkindex.users.models import Role
 from arkindex.users.utils import get_max_level
 
 ProcessFarmField = import_string(getattr(settings, "PROCESS_FARM_FIELD", None) or "arkindex.project.serializer_fields.NullField")
-get_default_farm = import_string(getattr(settings, "GET_DEFAULT_FARM", None) or "arkindex.process.utils.get_default_farm")
 
 
 class ProcessLightSerializer(serializers.ModelSerializer):