test format_exception too

Author: jepler

tests/circuitpython/traceback_test.py

@@ -21,7 +21,7 @@ def fun():
     print("\nLimit=0 Trace:")
     traceback.print_exception(None, exc, exc.__traceback__, limit=0)
     print("\nLimit=-1 Trace:")
-    traceback.print_exception(None, exc, exc.__traceback__, limit=-1)
+    print(traceback.format_exception(None, exc, exc.__traceback__, limit=-1))
 
 
 class NonNativeException(Exception):