Introduce pyupgrade

Closes #1742 (closed)

Introducing pyupgrade.

Again, I've made one commit per rule.

arkindex/training/api.py

@@ -737,7 +737,7 @@ class DatasetElementCursorPagination(CountCursorPagination):
     ordering = ("element_id", "id")
 
 
-class DatasetSetBase():
+class DatasetSetBase:
     permission_classes = (IsVerified, )
     serializer_class = DatasetSetSerializer