tests/basics: Unlock heap if skipping nanbox small-int test.

Signed-off-by: Damien George <damien@micropython.org>

tests/basics/nanbox_smallint.py

@@ -9,6 +9,7 @@ try:
     float(123)
     micropython.heap_unlock()
 except:
+    micropython.heap_unlock()
     print("SKIP")
     raise SystemExit