Fix compatibility issue of fluid.io.save_vars on windows platform (#19181)

python/paddle/fluid/io.py

@@ -222,13 +222,13 @@ def save_vars(executor,
                 continue
             new_var = _clone_var_in_block_(save_block, each_var)
             if filename is None:
+                save_file_path = os.path.join(save_dirname, new_var.name)
+                save_file_path = os.path.normpath(save_file_path)
                 save_block.append_op(
                     type='save',
                     inputs={'X': [new_var]},
                     outputs={},
-                    attrs={
-                        'file_path': os.path.join(save_dirname, new_var.name)
-                    })
+                    attrs={'file_path': save_file_path})
             else:
                 save_var_map[new_var.name] = new_var