[Chore]: fix brew workflow

[jsjoeio]

https://github.com/coder/code-server/runs/4974830516?check_suite_focus=true#step:5:142

[jsjoeio]

There are a couple places where we need to invert the logic

https://github.com/coder/code-server/blob/main/ci/steps/brew-bump.sh#L32

https://github.com/coder/code-server/blob/main/ci/steps/brew-bump.sh#L70

https://github.com/coder/code-server/blob/main/ci/steps/brew-bump.sh#L80

[jsjoeio]

fatal: unable to access 'https://github.com/cdrci/homebrew-core.git/': The requested URL returned error: 403

As you can see, this was not fixed in 4.2.0: https://github.com/coder/code-server/runs/5652853615?check_suite_focus=true#step:6:69

This is interesting because it worked on my fork under jsjoeio/code-server. I don't know if there's a permission needed under coder the GitHub org, or something related to cdrci.

I think the next steps are to try starting from scratch and using the --dry-run flag with the brew bump-formula-pr in code-server CI since we learned that running there vs. a fork's CI produces different results.

Thoughts

I'm guessing we need to overwrite GITHUB_TOKEN in CI when we run brew bump-formula-pr otherwise, it will use the author's GitHub creds, their homebrew-core fork and open the PR from them (which is not what we want).

[jsjoeio]

Based on this testing, I think I can open a PR to simplify the brew bump-formula-pr process.