Prior to being able to call `isatty()` or `ttyname()` on a new
subsidiary pty, the "ptem" module must be pushed there.

This patch comes from OmniOS.

--- Python-3.14.0/Lib/test/test_os.py.orig
+++ Python-3.14.0/Lib/test/test_os.py
@@ -4879,6 +4879,7 @@
         son_path = os.ptsname(mother_fd)
         son_fd = os.open(son_path, os.O_RDWR|os.O_NOCTTY)
         self.addCleanup(os.close, son_fd)
+        fcntl.ioctl(son_fd, fcntl.I_PUSH, "ptem")
         self.assertEqual(os.ptsname(mother_fd), os.ttyname(son_fd))
 
     @unittest.skipUnless(hasattr(os, 'spawnl'), "need os.spawnl()")