Introduce pyupgrade

Closes #1742 (closed)

Introducing pyupgrade.

Again, I've made one commit per rule.

arkindex/users/tests/test_jobs.py

@@ -32,7 +32,7 @@ class MockedJob:
 
     @classmethod
     def key_for(cls, id):
-        return f"rq:job:{id}".encode("utf-8")
+        return f"rq:job:{id}".encode()
 
 
 class TestJobs(FixtureAPITestCase):