Fix homebrew step in publish workflow

[jsjoeio]

Something went wrong when we tried to update cdrci's fork: https://github.com/cdr/code-server/runs/2643613944?check_suite_focus=true

We need to figure out how to do that correctly.

This might help: https://docs.github.com/en/github/authenticating-to-github/keeping-your-account-and-data-secure/creating-a-personal-access-token#using-a-token-on-the-command-line

echo "cdr\n$token" | git push might work as well.

[jsjoeio]

Going to see if I can replicate the issue locally by:

1. git clone https://github.com/cdrci/homebrew-core.git
2. git remote add upstream https://github.com/Homebrew/homebrew-core.git
3. git fetch upstream
4. git merge upstream/master
5. echo "cdr\n$token" | git push