Update app_jitk service status

New test was added in d2d47acdceff78baa1c8ca40f9cf88c4ceda8c87.
It fails - as many others - in `compiler == app_jitk` mode.

Change-Id: Id2ab4aec2e7f631a206490d46fefc614b4d666f5
Reviewed-on: https://dart-review.googlesource.com/62148
Reviewed-by: Jens Johansen <jensj@google.com>
diff --git a/runtime/observatory/tests/service/service_kernel.status b/runtime/observatory/tests/service/service_kernel.status
index 1786a6f..87f2e7f 100644
--- a/runtime/observatory/tests/service/service_kernel.status
+++ b/runtime/observatory/tests/service/service_kernel.status
@@ -101,6 +101,7 @@
 step_through_function_2_test: RuntimeError
 step_through_function_test: RuntimeError
 step_through_getter_test: RuntimeError
+step_through_mixin_from_sdk_test: RuntimeError
 step_through_property_get_test: RuntimeError
 step_through_property_set_test: RuntimeError
 step_through_setter_test: RuntimeError