Fix pull requests silently disappearing until lazygit is restarted

[stefanhaller]

A lazygit instance that has been open for a while sometimes stops showing pull requests, and keeps not showing them until you quit and restart it. The cause is that we resolve the GitHub token once per process and then keep using that stale answer.

We get the token from go-gh, which reads gh's hosts.yml on the first call and caches it for the lifetime of the process. gh rewrites that file whenever the active account changes, and keeps the active account's token either in the file or in the system keyring, depending on the account. Once the file changes under us, our snapshot no longer describes reality: either we keep sending a token for an account that is no longer active, or — if the snapshot was taken while a keyring-backed account was active — we find no token at all, drop the remote, and show no pull requests. Nothing is reported to the user, so it looks like PR fetching is simply broken.

Switching accounts with gh auth switch is the easiest way to trigger this, but it isn't limited to multi-account setups: a single account hits the same thing whenever its token is rotated, or moved between the keyring and hosts.yml by a fresh gh auth login.

So ask gh itself for the token on every refresh, with gh auth token --hostname <host>, which resolves it afresh from whichever of the environment, the keyring, or the config file currently holds it. Not passing --secure-storage (which go-gh does internally) also means it stops mattering which of the two the active account uses. go-gh's lookup stays as a fallback for setups without the gh binary, where it still picks up GH_TOKEN and friends; when gh is present it checks those variables itself.

To reproduce on master, with two gh accounts, one with its token in the keyring and one in hosts.yml: start lazygit while the keyring-backed account is active, then run gh auth switch to the other one. The pull request information disappears on the next refresh and doesn't come back until lazygit is restarted. Running gh auth token --secure-storage --hostname github.com by hand at that point prints no oauth token found for github.com.