Fix view_api bug where unnamed rotes where showing api_name instead of fn_index

[freddyaboulton]

Description

Long-winded title but the issue was that unnamed routes were shown with api_name='0' as opposed to fn_index=0, which caused user confusion.

client = Client("stabilityai/stable-diffusion") 
client.view_api()
Client.predict() Usage Info
---------------------------
Named API endpoints: 0

Unnamed API endpoints: 4

...
- predict(enter_your_prompt, enter_your_negative_prompt, guidance_scale, api_name="1") -> generated_images
    Parameters:
     - [Textbox] enter_your_prompt: str (string value)
     - [Textbox] enter_your_negative_prompt: str (string value)
     - [Slider] guidance_scale: int | float (numeric value)
    Returns:
     - [Gallery] generated_images: str (path to directory with images and a file associating images with captions called captions.json)
...

Checklist:

• I have performed a self-review of my own code
• I have added a short summary of my change to the CHANGELOG.md
• My code follows the style guidelines of this project
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

A note about the CHANGELOG

Hello 👋 and thank you for contributing to Gradio!

All pull requests must update the change log located in CHANGELOG.md, unless the pull request is labeled with the "no-changelog-update" label.

Please add a brief summary of the change to the Upcoming Release > Full Changelog section of the CHANGELOG.md file and include
a link to the PR (formatted in markdown) and a link to your github profile (if you like). For example, "* Added a cool new feature by [@myusername](link-to-your-github-profile) in [PR 11111](https://github.com/gradio-app/gradio/pull/11111)".

If you would like to elaborate on your change further, feel free to include a longer explanation in the other sections.
If you would like an image/gif/video showcasing your feature, it may be best to edit the CHANGELOG file using the
GitHub web UI since that lets you upload files directly via drag-and-drop.

[gradio-pr-bot]

All the demos for this PR have been deployed at https://huggingface.co/spaces/gradio-pr-deploys/pr-3972-all-demos

[abidlabs]

Suggestion, maybe just check if "fn_index=0" is in the string, as the format of the view_api(return_format="str") may change and we don't want this test to be welded too tightly to the format

(this would also fix the failing test)

[freddyaboulton]

Fixed now @abidlabs ! Thanks

[abidlabs]

Thanks @freddyaboulton for the fix!