minor fix to render failure in depcrecation warning (#3471)

Author: yiming0416

advanced_source/cpp_export.rst

@@ -1,3 +1,3 @@
 .. warning::
     TorchScript is deprecated, please use 
-    `torch.export<https://docs.pytorch.org/tutorials/intermediate/torch_export_tutorial.html>`_ instead.
+    `torch.export <https://docs.pytorch.org/tutorials/intermediate/torch_export_tutorial.html>`__ instead.

advanced_source/torch_script_custom_ops.rst

@@ -3,4 +3,4 @@
 
 .. warning::
     TorchScript is deprecated, please use 
-    `torch.export<https://docs.pytorch.org/tutorials/intermediate/torch_export_tutorial.html>`_ instead.
+    `torch.export <https://docs.pytorch.org/tutorials/intermediate/torch_export_tutorial.html>`__ instead.