[Cherry pick] rename BoundingBoxes module to match class name (#7910) (#7918)

Co-authored-by: Philip Meier <[email protected]>

Author: NicolasHug

torchvision/tv_tensors/__init__.py

@@ -1,6 +1,6 @@
 import torch
 
-from ._bounding_box import BoundingBoxes, BoundingBoxFormat
+from ._bounding_boxes import BoundingBoxes, BoundingBoxFormat
 from ._image import Image
 from ._mask import Mask
 from ._torch_function_helpers import set_return_type