endtoend: Combine output file name tests (#1000)

Author: kyleconroy

internal/endtoend/testdata/output_db_file_name/go/models.go

@@ -7,6 +7,8 @@
       "schema": "query.sql",
       "queries": "query.sql",
       "emit_interface": true,
+      "output_db_file_name": "db_gen.go",
+      "output_models_file_name": "models_gen.go",
       "output_querier_file_name": "querier_gen.go"
     }
   ]