Move rescale dtype recasting to match torchvision ToTensor
# What does this PR do?

The dtype casting of the input image when rescaling was moved in #25174 so that precision was kept when rescaling if desired. However, this broke equivalence tests with torchvision's `ToTensor` transform c.f. [this comment](https://github.com/huggingface/transformers/pull/24796#issuecomment-1657275333).


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?
_The documentation is not available anymore as the PR was closed or merged._<|||||>Thank you very much, Amy!