Fix typos in Sound API documentation

[pushfoo]

Broken Reference in arcade.load_sound's return doc

This needs s/ref:/:ref:/:

The Callout Boxes Have Typos

The same typos is repeated in the following doc (needs s/py;/py:):

1. Sound.play
2. arcade.load_sound()
3. arcade.play_sound()

[Adithya1331]

Hi! I’d like to work on this documentation fix. Could I be assigned?

[pushfoo]

@Adithya1331 yep! Sphinx ReST can be a little weird so feel free to ask for help. This heading will be useful for getting started:
https://github.com/pythonarcade/arcade/blob/development/CONTRIBUTING.md#building--testing-documentation