Tell git not to use my GitHub account (Keychain) for public repositories - it's a privacy issue
Add the variable HOMEBREW_NO_GITHUB_API to your environment.

For example add this to your .bash_profile to turn off "once for all":

export HOMEBREW_NO_GITHUB_API=1


or put it in front of the brew for single actions:

HOMEBREW_NO_GITHUB_API=1 brew search geoip