nix: add new loadtest for errors

Also included it in CI.

test/load/errors.sql

@@ -0,0 +1,7 @@
+\ir fixtures.sql
+
+SELECT format('CREATE TABLE test.actors_%s ();', n)
+FROM generate_series(1, 20000) n
+\gexec
+
+-- TODO add many function for fuzzy search (somehow this is making the loadtest start slow)