[3.15] gh-154414: Skip test_tcsendbreak on DragonFly BSD (GH-154415) (GH-154426)

tcsendbreak() is not supported for pseudo-terminals on DragonFly BSD.
(cherry picked from commit a84e780)

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

Author: serhiy-storchaka

Lib/test/test_termios.py

@@ -104,7 +104,7 @@ def test_tcsendbreak(self):
         try:
             termios.tcsendbreak(self.fd, 1)
         except termios.error as exc:
-            if exc.args[0] == errno.ENOTTY and sys.platform.startswith(('freebsd', 'netbsd', 'openbsd')):
+            if exc.args[0] == errno.ENOTTY and sys.platform.startswith(('freebsd', 'netbsd', 'openbsd', 'dragonfly')):
                 self.skipTest('termios.tcsendbreak() is not supported '
                               'with pseudo-terminals (?) on this platform')
             raise