Update PyTorch example to support 2.3.0 (#2257)

Colab by default ships with outdated versions of `torch` and
`torchvision` (given that they just released a new version on 4/24/24).
Adding this explicit upgrade to pip will keep these tutorials more
stable.

Also it turns out that dynamic shape export wasn't backported into the
2.3 release cut, so while this does work at nightly, it still won't be
tested in the 2.3 colab, updated wording to specify 2.4.