fix link

Author: matsumotosan

src/lightning/fabric/plugins/io/checkpoint_io.py

@@ -60,7 +60,7 @@ def load_checkpoint(
             primitive types. If loading a checkpoint from a trusted source that contains an ``nn.Module``, use
                 ``weights_only=False``. If loading checkpoint from an untrusted source, we recommend using
                 ``weights_only=True``. For more information, please refer to the
-                `PyTorch Developer Notes on Serialization Semantics <https://docs.pytorch.org/docs/main/notes/serialization.html#id3>`__.
+                `PyTorch Developer Notes on Serialization Semantics <https://docs.pytorch.org/docs/main/notes/serialization.html#id3>`_.
 
         Returns: The loaded checkpoint.