The 'site-update' option of drupal:site-install seems to have no effect

[donquixote]

For development installations, the update module is kinda useless.
Arguably it is also useless in sites managed by composer, if developers and the sec team are responsible of keeping packages up to date. But this could be debated.

It seems that the drupal:site-install command already has an option to disable installation of the update module.
I see a cli parameter site-update.
I also see drupal.site.update: false in runner.yml, which implies that the default is already to not enable this.

However, it seems this setting has no effect, and the update module is installed either way.

Am I missing something?