Fix for `typing.get_type_hints()` on Python 3.9 or lower (#4228)
* fix
* fix docstring
* type hint fix
* fix test
* Update gradio/utils.py
Co-authored-by: Aarni Koskela <akx@iki.fi>
* fix indentation
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Co-authored-by: Aarni Koskela <akx@iki.fi>
