Homebrew revises update process at GitHub's request

Very recent Homebrew updates may fail with error messages about "shallow" clones. GitHub has requested this as these are said to be extremely expensive operations. Mitigations are discussed and the solution revealed here: https://github.com/Homebrew/brew/pull/9383 https://github.com/Homebrew/discussions/discussions/225 https://github.com/Homebrew/discussions/discussions/226