Fix backport of test_curses test skip.

Lib/test/test_curses.py

@@ -270,7 +270,7 @@ if __name__ == '__main__':
     unit_tests()
 else:
     if not sys.__stdout__.isatty():
-        raise unittest.SkipTest("sys.__stdout__ is not a tty")
+        raise TestSkipped("sys.__stdout__ is not a tty")
     # testing setupterm() inside initscr/endwin
     # causes terminal breakage
     curses.setupterm(fd=sys.__stdout__.fileno())