Fix some deprecation warnings from PyTorch

[fmassa]

Fixes some warnings that showed up in tests, see https://app.circleci.com/pipelines/github/pytorch/vision/6141/workflows/f4504c18-123c-483a-be33-e33b92997f42/jobs/398743 for some examples

The tests that had those warnings were

test/test_transforms_video.py::TestVideoTransforms::test_random_resized_crop_video
  /root/project/env/lib/python3.7/site-packages/torch/nn/functional.py:3463: UserWarning: Default upsampling behavior when mode=bilinear is changed to align_corners=False since 0.4.0. Please specify align_corners=True if the old behavior is desired. See the documentation of nn.Upsample for details.

and

test/test_models_detection_negative_samples.py::Tester::test_forward_negative_sample_retinanet
  /root/project/env/lib/python3.7/site-packages/torch/nn/_reduction.py:42: UserWarning: size_average and reduce args will be deprecated, please use reduction='sum' instead.
    warnings.warn(warning.format(ret))

[datumbox]

LGTM thanks.