Close the pty master before the slave in ScreenTests

On macOS, closing the pty slave while the master is still open blocks until
the slave's pending output drains.  Closing the master first stops the reader
thread and leaves nothing for the slave close to wait for.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_curses.py

@@ -1795,16 +1795,17 @@ def _drain_pty(master):
 
     def make_pty(self):
         master, slave = os.openpty()
-        # Nothing reads the master end, so writing to the slave -- and the
-        # tcdrain() inside endwin() -- can block once the pty buffer fills (on
-        # macOS, not Linux).  Drain it from a background thread; endwin()
-        # releases the GIL so the thread runs while endwin() blocks.
+        # Nothing reads the master end, so writing to the slave and the
+        # tcdrain() in endwin() can block on macOS once the pty buffer fills;
+        # drain it from a background thread (endwin() releases the GIL).
         reader = threading.Thread(target=self._drain_pty, args=(master,),
                                   daemon=True)
         reader.start()
         self.addCleanup(reader.join, SHORT_TIMEOUT)
-        self.addCleanup(os.close, master)
+        # Close the master first (cleanups run in reverse): on macOS, closing
+        # the slave first blocks until its pending output drains.
         self.addCleanup(os.close, slave)
+        self.addCleanup(os.close, master)
         return slave
 
     def test_newterm(self):