Homebrew’s brew cleanup saves disk space by deleting old versions of packages. From time to time, CI macOS images get out of date with Homebrew, and auto-cleanup is triggered unintentionally upon brew install during a CI run. There is no benefit to this on CI.

Disable Homebrew auto cleanup by setting environment variable HOMEBREW_NO_INSTALL_CLEANUP=1. On GitHub Actions, this is accomplished near the top of the particular .github/workflows/*.yml file:

env:
   HOMEBREW_NO_INSTALL_CLEANUP: 1