utils/github: use x-access-token

[Bo98]

This is mandatory for GitHub App tokens.

It seems to also work for PATs - documentation isn't exactly clear on that but I think it works.

Probably fixes Homebrew/actions#584

[Goooler]

LGTM.

https://docs.github.com/en/apps/creating-github-apps/authenticating-with-a-github-app/authenticating-as-a-github-app-installation#about-authentication-as-a-github-app-installation

[MikeMcQuaid]

Thanks @Bo98, let's give it a whirl.

[Goooler]

Error: Failure while executing; `/usr/bin/env git push --set-upstream ***github.com/Goooler/homebrew-repo bump-kotlin-explorer-1.6.0:bump-kotlin-explorer-1.6.0` exited with 1. Here's the output:
To https://github.com/Goooler/homebrew-repo
 ! [rejected]        bump-kotlin-explorer-1.6.0 -> bump-kotlin-explorer-1.6.0 (non-fast-forward)
error: failed to push some refs to 'https://github.com/Goooler/homebrew-repo'

https://github.com/Goooler/homebrew-repo/actions/runs/10700380504/job/29663997922

Originally posted by @Goooler in Homebrew/actions#584 (comment)