Expose missing fill method in global_rng module

[TheJokr]

I recently had a use case for Rng::fill, but had to instantiate a new Rng because the method isn't exposed from the crate's global one. All the other Rng methods are present in mod global_rng, so I figured it's an oversight.

[TheJokr]

Looks like rustsec/audit-check renamed their master branch to main, which makes the CI pipeline fail. I updated the reference and made it work again.