tests: arm: exclude mps2/an385 on user stack test

Temporarily disable running the user stack tests on mps2/an385 to
unblock ci issues reported in #98494.

Signed-off-by: Sudan Landge <[email protected]>

Author: wearyzen

tests/arch/arm/arm_user_stack_test/testcase.yaml

@@ -2,6 +2,9 @@ common:
   tags:
     - arm
   timeout: 120
+  # TODO: remove the platform_exclude once the issue with MPS2/AN385 is fixed.
+  platform_exclude:
+    - mps2/an385
 tests:
   arch.arm.user.stack:
     filter: CONFIG_CPU_CORTEX_M