fix: Put a fallback ansible path in place

In the past we installed ansible using pip install --user, however since
Debian 12/Python 3.11 encourage us rightly not do this, we migrate to a
custom venv. However, old installations don't have this, so we fall back
to the old path.

upgrade.sh

@@ -49,6 +49,9 @@ yesno_prompt() {
 }
 
 do_upgrade() {
+    if [ ! -f "$ansible_bin_path/ansible" ]; then
+      ansible_bin_path="$HOME/.local/bin"
+    fi
     echo '[Beginning upgrade]'
     playbook_path="$ansible_conf_path/playbook.yml"
     echo "[1/$total_steps] Retrieving currently installed version from $playbook_path"