relnotes doesn't ~~work~~ give a good error message with fine-grained API Token

[ComputerDruid]

GitHub has launched Fine-grained personal access tokens, but they apparently don't work with the GraphQL API yet

That's not really a problem, since you can still generate and use a classic token. But the error message is a little hard to diagnose:

$ cargo run --release 1.68.0 | tee notes.md
    Finished release [optimized] target(s) in 0.09s
     Running `target/release/relnotes 1.68.0`
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/main.rs:177:52
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The json it's giving back turns out to be:

{"documentation_url":"https://docs.github.com/graphql/guides/forming-calls-with-graphql#authenticating-with-graphql","message":"Personal access tokens with fine grained access do not support the GraphQL API"}

Which is easy enough to understand, we should probably just surface that somewhere.