Fix bug in Textual Inversion Unloading (#9304)
* Update textual_inversion.py
* add unload test
* add comment
* fix style
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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: Your Name <you@example.com>
Co-authored-by: YiYi Xu <yixu310@gmail.com>
