style: format backend with black

Also drops the session-sliding comment in login_required.

backend/tests/test_app.py

@@ -16,7 +16,9 @@ class AppTests(ApiTestCase):
         db_execute(SCHEMA.read_text())
         db_execute(SCHEMA.read_text())
         self.assertEqual(db_execute("SELECT count(*) FROM genres")[0][0], 16)
-        self.assertEqual(db_execute("SELECT last_value FROM genres_id_seq")[0][0], before)
+        self.assertEqual(
+            db_execute("SELECT last_value FROM genres_id_seq")[0][0], before
+        )
 
     def test_unknown_route_returns_json_404(self):
         response = self.call("GET", "/api/nope")
@@ -24,7 +26,9 @@ class AppTests(ApiTestCase):
         self.assertIn("error", response.get_json())
 
     def test_mutation_without_json_content_type_is_rejected(self):
-        response = self.client.post("/api/health", data="x", content_type="text/plain", base_url=HTTPS)
+        response = self.client.post(
+            "/api/health", data="x", content_type="text/plain", base_url=HTTPS
+        )
         self.assertEqual(response.status_code, 400)
         self.assertEqual(
             response.get_json(),
@@ -32,6 +36,10 @@ class AppTests(ApiTestCase):
         )
 
     def test_oversized_body_is_rejected_before_parsing(self):
-        response = self.call("POST", "/api/auth/login", {"username": "a", "password": "x" * (2 * 1024 * 1024)})
+        response = self.call(
+            "POST",
+            "/api/auth/login",
+            {"username": "a", "password": "x" * (2 * 1024 * 1024)},
+        )
         self.assertEqual(response.status_code, 413)
         self.assertIn("error", response.get_json())