Move apt-get update before the 'already installed' check so the
package index is always refreshed. Previously, on environments like
Codespaces where base packages are pre-installed, the update was
skipped entirely, causing downstream scripts (e.g. 23-stow.sh) to
fail with 'Unable to locate package'.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
