fix: make repo update idempotent

tasks/install_packages.yml

 ---
-# Äquivalent von apt-get update
+# Equivalent of apt-get update
+# Out of sheer dumb luck, this might not be idempotent if the distro repo info
+# is updated even between two CI runs. We'll skip the check.
 - name: apt-get update
   ansible.builtin.apt:
     update_cache: true
   when: ansible_os_family == "Debian"
+  changed_when: false
 
 # Äquivalent von dnf update
 - name: update packages (RedHat)