Fix outdated Gradio API usage in GAN guide (#13604)
The "Create your own friends with a GAN" guide still used the 2.x
Slider API: gr.Slider(..., default=...) raises TypeError on current
Gradio because the kwarg is now called value. The default= kwarg was
left behind when #1796 replaced gr.inputs.Slider with gr.Slider.
The guide also passed cache_examples=True to .launch(), but
cache_examples is a gr.Interface parameter and Blocks.launch() does
not accept it, so the full-code example failed even with the slider
fix. Move it into the gr.Interface(...) call.
Fixes #13603
