tests: Activate recursive_data.py test, now that io.StringIO is available.

tests/misc/recursive_data.py_ → tests/misc/recursive_data.py

 # This tests that printing recursive data structure doesn't lead to segfault.
-# Unfortunately, print() so far doesn't support "file "kwarg, so variable-len
-# output of this test cannot be redirected, and this test cannot be validated.
+import _io as io
+
 l = [1, 2, 3, None]
 l[-1] = l
 try:
-    print(l)
+    print(l, file=io.StringIO())
 except RuntimeError:
     print("RuntimeError")

tests/misc/recursive_data.py.exp

+RuntimeError