tests/micropython: Move alloc-less traceback test to separate test file.

The native emitter doesn't provide proper traceback info so this test
should not be run in that case.

tests/micropython/heapalloc_traceback.py

@@ -0,0 +1,24 @@
+# test that we can generate a traceback without allocating
+
+import micropython
+import sys
+
+# preallocate exception instance with some room for a traceback
+global_exc = StopIteration()
+try:
+    raise global_exc
+except:
+    pass
+
+def test():
+    global global_exc
+    global_exc.__traceback__ = None
+    try:
+        raise global_exc
+    except StopIteration as e:
+        sys.print_exception(e)
+
+# call test() with heap allocation disabled
+micropython.heap_lock()
+test()
+micropython.heap_unlock()