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From time to time, CI MacOS images get out of date with Homebrew, and auto-cleanup is triggered unintentionally upon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
On GitHub Actions, this is accomplished near the top of the particular .github/workflows/*.yml file:
env: HOMEBREW_NO_INSTALL_CLEANUP: 1