Add str type annotation to device parameter in ToTensorD (#6737)

### Description

A simple fix adding `str` type annotation to the `device` parameter in
`ToTensorD`, making it consistent with `ToTensor`. As this fix is very
simple, I hope it's okay I don't create an issue in advance.

Signed-off-by: function2 <function2-llx@outlook.com>

monai/transforms/utility/dictionary.py

@@ -514,7 +514,7 @@ def __init__(
         self,
         keys: KeysCollection,
         dtype: torch.dtype | None = None,
-        device: torch.device | None = None,
+        device: torch.device | str | None = None,
         wrap_sequence: bool = True,
         track_meta: bool | None = None,
         allow_missing_keys: bool = False,