gh-154345: Fix test_posix_pty_functions() killing the worker on Solaris (GH-154346)

Pushing the "ptem" STREAMS module makes a session leader without a
controlling terminal acquire the slave as one, so closing the file
descriptors sent SIGHUP to the session and killed the regrtest worker.
Disown it after the pushes, as os.openpty() does.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_os/test_os.py

@@ -4728,12 +4728,27 @@ def test_posix_pty_functions(self):
         son_fd = os.open(son_path, os.O_RDWR|os.O_NOCTTY)
         self.addCleanup(os.close, son_fd)
         if sys.platform.startswith('sunos'):
-            # The slave is not a terminal until these STREAMS modules
-            # are pushed onto it.
             import fcntl
             I_PUSH = 0x5302
+            TIOCNOTTY = 0x7471
+            # Pushing "ptem" makes the slave a terminal, which a session
+            # leader without a controlling terminal then acquires as one
+            # despite O_NOCTTY.  Note whether we already had one.
+            try:
+                os.close(os.open('/dev/tty', os.O_RDONLY|os.O_NOCTTY))
+                had_ctty = True
+            except OSError:
+                had_ctty = False
             fcntl.ioctl(son_fd, I_PUSH, b'ptem\0')
             fcntl.ioctl(son_fd, I_PUSH, b'ldterm\0')
+            if not had_ctty and os.getsid(0) == os.getpid():
+                # Disown it, otherwise closing the file descriptors sends
+                # SIGHUP to the session.  TIOCNOTTY sends it too.
+                old_handler = signal.signal(signal.SIGHUP, signal.SIG_IGN)
+                try:
+                    fcntl.ioctl(son_fd, TIOCNOTTY)
+                finally:
+                    signal.signal(signal.SIGHUP, old_handler)
         self.assertEqual(os.ptsname(mother_fd), os.ttyname(son_fd))
 
     @warnings_helper.ignore_fork_in_thread_deprecation_warnings()