Introduce pyupgrade

Closes #1742 (closed)

Introducing pyupgrade.

Again, I've made one commit per rule.

arkindex/training/management/commands/migrate_workers.py

@@ -46,7 +46,7 @@ def choose(instances, name_field="name", title="Pick one item", allow_skip=False
         choices["0"] = choices["skip"] = None
     for i, (id, name) in enumerate(items, 1):
         print(f"{i}: {id} {name}")
-        choices[str((i))] = choices[str(id)] = choices[name] = id
+        choices[str(i)] = choices[str(id)] = choices[name] = id
 
     # Get the first valid choice
     while True: