tests: arm_no_multithreading: move to new API

Make test use new API.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/tests/arch/arm/arm_no_multithreading/prj.conf b/tests/arch/arm/arm_no_multithreading/prj.conf
index 33e8aeb..65dd4e5 100644
--- a/tests/arch/arm/arm_no_multithreading/prj.conf
+++ b/tests/arch/arm/arm_no_multithreading/prj.conf
@@ -1,4 +1,5 @@
 CONFIG_ZTEST=y
+CONFIG_ZTEST_NEW_API=y
 CONFIG_MULTITHREADING=n
 CONFIG_ASSERT=y
 CONFIG_FPU=y