Fix: add clamping to avoid v2.ElasticTransform IndexError when bbox equals canvas size

[jsalvasoler]

elastic_bounding_boxes used bbox corner coordinates as direct indices into inv_grid (shape 1×H×W×2) without
clamping. After ceil_(), a coordinate equal to W or H (e.g. a box touching the image edge) produced index W/H,
which is out of bounds.

Fix: clamp index_x and index_y to [0, W-1] / [0, H-1] before the grid lookup, identical to the clamping already
present in elastic_keypoints

vision/torchvision/transforms/v2/functional/_geometry.py

Lines 2398 to 2399 in 6d85459

	index_x.clamp_(0, inv_grid.shape[2] - 1)
	index_y.clamp_(0, inv_grid.shape[1] - 1)

This was the fix suggested by @zy1git on the issue thread.
Let me know if you want me to add a test to test/test_transforms_v2.py

Fixes #9394

[pytorch-bot]

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[zy1git]

@jsalvasoler Thanks a lot for creating this PR! Feel free to add a test and I will review it.

[jsalvasoler]

@jsalvasoler Thanks a lot for creating this PR! Feel free to add a test and I will review it.

@zy1git test is added!

[NicolasHug]

We only need to call F.elastic_bounding_boxes, going through check_kernel is a bit overkill for this test.

[jsalvasoler]

Thanks for the feedback! Already updated.

[github-actions]

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