tests/micropython: Add missing SystemExit after printing SKIP.

The test runner expects `print("SKIP")` to be followed by
`raise SystemExit`.  Otherwise it waits for 10 seconds for the target to
do a soft reset before timing out and continuing.

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

tests/micropython/meminfo.py

@@ -5,7 +5,8 @@ import micropython
 # these functions are not always available
 if not hasattr(micropython, "mem_info"):
     print("SKIP")
-else:
+    raise SystemExit
+
 micropython.mem_info()
 micropython.mem_info(1)
 micropython.qstr_info()

tests/micropython/memstats.py

@@ -5,7 +5,8 @@ import micropython
 # these functions are not always available
 if not hasattr(micropython, "mem_total"):
     print("SKIP")
-else:
+    raise SystemExit
+
 t = micropython.mem_total()
 c = micropython.mem_current()
 p = micropython.mem_peak()

tests/micropython/stack_use.py

@@ -3,5 +3,6 @@ import micropython
 
 if not hasattr(micropython, "stack_use"):
     print("SKIP")
-else:
+    raise SystemExit
+
 print(type(micropython.stack_use()))  # output varies