Introduce pyupgrade

arkindex/documents/date_parser.py

arkindex/documents/dates.py

arkindex/documents/indexer.py

...dex/documents/management/commands/move_lines_to_parent.py

arkindex/documents/managers.py

arkindex/documents/models.py

arkindex/documents/serializers/elements.py

arkindex/documents/serializers/ml.py

arkindex/documents/tests/commands/test_load_export.py

arkindex/documents/tests/test_bulk_classification.py

arkindex/documents/tests/test_classes.py

arkindex/documents/tests/test_edit_elementpath.py

arkindex/documents/tests/test_element_paths_api.py

arkindex/images/management/commands/check_images.py

arkindex/images/models.py

arkindex/images/tests/test_image_api.py

arkindex/images/views.py

arkindex/ponos/models.py

arkindex/ponos/serializer_fields.py

arkindex/ponos/tasks.py