tests: thread_metric: Disable memory slab ptr validation

Disabling the memory slab pointer validation improves the performance
of the memory allocation sub-test by about 9%.

Signed-off-by: Peter Mitsis <[email protected]>

Author: peter-mitsis

tests/benchmarks/thread_metric/prj.conf

@@ -23,3 +23,6 @@ CONFIG_PICOLIBC_USE_MODULE=y
 
 # Disable Thread Local Storage for better context switching times
 CONFIG_THREAD_LOCAL_STORAGE=n
+
+# Disable memory slab pointer validation
+CONFIG_MEM_SLAB_POINTER_VALIDATE=n