Craft Docker container auth: credentials come from volume-mounted git config

When Craft runs inside Docker in CI (via getsentry/craft:latest), git authentication comes from actions/checkout's http.extraheader in the local .git/config, which is volume-mounted into the container at /github/workspace. The container sets HOME=/root, so global git config from the host runner isn't available. The GITHUB_TOKEN env var is passed separately. Craft's handleReleaseBranch() doesn't set up its own auth — it relies on whatever git config is present. Other targets (registry, commitOnGitRepository) explicitly inject tokens into clone URLs via GitHubRemote.getRemoteStringWithAuth() or URL manipulation.