Skip test_flush_return_value on linux platform

Author: killme2008

Lib/test/test_mmap.py

@@ -728,6 +728,7 @@ def test_concat_repeat_exception(self):
         with self.assertRaises(TypeError):
             m * 2
 
+    @unittest.skipIf(sys.platform.startswith("linux"), "TODO: RUSTPYTHON, memmap2 doesn't throw OSError when offset is not a multiple of mmap.PAGESIZE on Linux")
     def test_flush_return_value(self):
         # mm.flush() should return None on success, raise an
         # exception on error under all platforms.