Restores the enterprise-extensions install step (install:ee) and stops it
hanging during "Installing Grist".
install:ee clones the private grist-ee repo and falls back to a public
prebuilt tarball when the clone fails. On a host with an attached terminal
and no signed-in GitHub user, git does not fail - it blocks on
"Username for 'https://github.com':", so the install hangs forever.
GIT_TERMINAL_PROMPT=0 makes the clone fail fast so the tarball fallback
runs as intended.
Refs community-scripts/ProxmoxVE#14782
