[CI] Fix incorrectly named test module for Hunyuan DiT

[DN6]

What does this PR do?

Test module is called hunyuan_dit while the pipleline module is hunyuandit. These need to match for the pipe test fetcher can run the appropriate test module.

The test isn't running because of this:
https://github.com/huggingface/diffusers/actions/runs/13452280062/job/37588801420#step:7:32

Fixes # (issue)

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[hlky]

Thanks @DN6