test_start_next_batch_build_repo_building: actually try to start the batch

tests/test_scheduler/test_batches.py

@@ -421,6 +421,8 @@ class TestBatches:
         builder = mock.MagicMock()
         builder.buildroot_ready.return_value = False
 
+        start_next_batch_build(conf, module_build, builder)
+
         module_build = models.ModuleBuild.get_by_id(db_session, 3)
 
         # Batch number should not increase.