test: Make failing loadtest fixtures pass again

PR #2358 added a bulk insert to the loadtest. However this broke the regular insert test,
which just returned 400 Bad Request because of a missing PK value since. Adding the new
id column in the payload to the ?columns= argument fixes that.

test/load/fixtures.sql

@@ -13,7 +13,7 @@ INSERT INTO test.actors VALUES (1, 'John Doe');
 
 -- POST target needs generated PK
 CREATE TABLE test.films (
-  id  INT PRIMARY KEY,
+  id INT PRIMARY KEY,
   title TEXT,
   year TEXT,
   runtime TEXT,