tests/micropython/heapalloc_fail_set.py: Remove extra trailing comma.

Unlike tuples, sets do not need trailing comma when there is only one item.

tests/micropython/heapalloc_fail_set.py

@@ -6,7 +6,7 @@ import micropython
 x = 1
 micropython.heap_lock()
 try:
-    {x,}
+    {x}
 except MemoryError:
     print('MemoryError: set create')
 micropython.heap_unlock()