This matches the other saving-related methods for Gdk.Pixbuf
- `gdk_pixbuf_save_to_stream` was skipped for the auto-generated bindings (with the warning "Ellipsis parameter: hide and bind manually")
- `gdk_pixbuf_save_to_streamv` was in the generated bindings, but incorrect: the `option_keys` and `option_values` arguments had type `string` rather than `string[]`
