Load custom model for faster tests

[danbraunai-apollo]

Some tests make use of tests.utils.get_tinystories_config and load tinystories-1m from the internet. This makes the tests slow.

These tests could instead use a locally saved model (e.g. this model) which would be much faster.

Also, huggingface is commonly down, which causes all of the current tests that read from huggingface to fail.