fix expand rust macro

[getong]

when using lsp-bridge-rust-expand-macro command
error msg

Error when processing response 4247
Traceback (most recent call last):
  File "/Users/a/.emacs.d/var/straight/repos/lsp-bridge/core/handler/__init__.py", line 38, in handle_response
    self.process_response(response)
  File "/Users/a/.emacs.d/var/straight/repos/lsp-bridge/core/handler/rust_expand_macro.py", line 15, in process_response
    eval_in_emacs("lsp-bridge-rust-expand-macro--update", response["name"], response["expansion"])
TypeError: 'NoneType' object is not subscriptable

[manateelazycat]

Thanks