Add parameter type to to_tensor (#8251)

Co-authored-by: Nicolas Hug <[email protected]>

torchvision/transforms/functional.py

@@ -8,6 +8,7 @@
 import numpy as np
 import torch
 from PIL import Image
+from PIL.Image import Image as PILImage
 from torch import Tensor
 
 try:
@@ -123,7 +124,7 @@ def _is_numpy_image(img: Any) -> bool:
     return img.ndim in {2, 3}
 
 
-def to_tensor(pic) -> Tensor:
+def to_tensor(pic: Union[PILImage, np.ndarray]) -> Tensor:
     """Convert a ``PIL Image`` or ``numpy.ndarray`` to tensor.
     This function does not support torchscript.