bpo-42789: Enable using /dev/tty in test_curses. (GH-24085)

It was temporary disabled for debugging.
diff --git a/Lib/test/test_curses.py b/Lib/test/test_curses.py
index 31fb882..7b40d71 100644
--- a/Lib/test/test_curses.py
+++ b/Lib/test/test_curses.py
@@ -85,7 +85,7 @@ def setUp(self):
             else:
                 try:
                     # Try to open the terminal device.
-                    tmp = open('/xdev/tty', 'wb', buffering=0)
+                    tmp = open('/dev/tty', 'wb', buffering=0)
                 except OSError:
                     # As a fallback, use regular file to write control codes.
                     # Some functions (like savetty) will not work, but at