Support fetching Bun from GitHub

[sebdanielsson]

In corporate networks with restrictions on outgoing traffic it would help if setup-bun could automatically fetch the specified version from GitHub Releases instead of bun.sh since connections to github is already allowed.

[xhyrom]

This is something that was implemented by #93, but unfortunately was closed by core team.

https://github.com/oven-sh/setup-bun/issues/37#issuecomment-2256820622dô

[sebdanielsson]

@Jarred-Sumner thoughts?👀

[xhyrom]

@Jarred-Sumner thoughts?👀

If you need this, you can use bun-download-url as workaround - https://github.com/oven-sh/setup-bun?tab=readme-ov-file#override-download-url