Update SwinForMaskedImageModeling doctest values
# What does this PR do?

Doc test was failing because checkpoints were changed in #20034 which have different config values, resulting in different image sizes after preprocessing. 

* Previous config: https://huggingface.co/microsoft/swin-tiny-patch4-window7-224/blob/main/preprocessor_config.json
* New config: https://huggingface.co/microsoft/swin-base-simmim-window6-192/blob/main/preprocessor_config.json

Updates the test to reflect the new checkpoints. 

## 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._