gh-127906: Add missing sys import to test_cppext (GH-132902)

(cherry picked from commit 9cba148)

Co-authored-by: Victor Stinner <[email protected]>

Author: vstinner

Lib/test/test_cppext/setup.py

@@ -3,6 +3,7 @@
 import os
 import platform
 import shlex
+import sys
 import sysconfig
 from test import support