Fix imagefolder with one image
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6556). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. Fixed in dataset viewer: https://huggingface.co/datasets/multimodalart/repro_1_image

<img width="682" alt="Capture d’écran 2024-02-12 à 22 57 08" src="https://github.com/huggingface/datasets/assets/1676121/be9a8dbc-2d78-4ffc-aed4-293a7c57bc0d">

A dataset repository with one image and one metadata file was considered a JSON dataset instead of an ImageFolder dataset. This is because we pick the dataset type with the most compatible data file extensions present in the repository and it results in a tie in this case.

e.g. for https://huggingface.co/datasets/multimodalart/repro_1_image

I fixed this by deprioritizing metadata files in the count.

fix https://github.com/huggingface/datasets/issues/6545