gh-63016: fix failing mmap.flush tests on FreeBSD (#143230)

Fix `mmap.flush` tests introduced in 1af21ea
where some flag combinations are not supported on FreeBSD.

Author: aisk

Lib/test/test_mmap.py

@@ -1173,7 +1173,13 @@ def test_flush_parameters(self):
             if hasattr(mmap, 'MS_INVALIDATE'):
                 m.flush(PAGESIZE * 2, flags=mmap.MS_INVALIDATE)
             if hasattr(mmap, 'MS_ASYNC') and hasattr(mmap, 'MS_INVALIDATE'):
-                m.flush(0, PAGESIZE, flags=mmap.MS_ASYNC | mmap.MS_INVALIDATE)
+                if sys.platform == 'freebsd':
+                    # FreeBSD doesn't support this combination
+                    with self.assertRaises(OSError) as cm:
+                        m.flush(0, PAGESIZE, flags=mmap.MS_ASYNC | mmap.MS_INVALIDATE)
+                    self.assertEqual(cm.exception.errno, errno.EINVAL)
+                else:
+                    m.flush(0, PAGESIZE, flags=mmap.MS_ASYNC | mmap.MS_INVALIDATE)
 
     @unittest.skipUnless(sys.platform == 'linux', 'Linux only')
     @support.requires_linux_version(5, 17, 0)