Default value for token added

[pseusys]

Closes #31 issue

[dsaltares]

First, thanks for the PR!

Are you sure this works?
Most actions that require the Github token force you to make it explicit. For example: https://github.com/marketplace/actions/godot-export#environment-variables.
IIRC I tested to default it and it didn't work.

[pseusys]

I'm not sure my code works, but I know and love an action that uses github token imlicitly.
And this is the code it uses: https://github.com/JamesIves/github-pages-deploy-action/blob/5a8b8e44c56b854f94bbb8d1e215518705b97a32/action.yml#L21-L32

[dsaltares]

Could you please make sure the action works with the implicit token? Once you test it, I'd be happy to get it merged!

[pseusys]

I've tried to run your test file without specifying token explicitly, here are the results: https://github.com/pseusys/fetch-gh-release-asset/actions/workflows/demo.yml

[dsaltares]

Thanks!