Add changed detection

tasks/main.yml

 - name: PREREQUIREMENTS | Update package index
   raw: pacman -Sy
+  register: command_res
+  changed_when: false
 
 - name: PREREQUIREMENTS | Install packages
-  raw: pacman --noconfirm -S {{ item }}
+  raw: pacman --needed --noconfirm -S {{ item }}
   with_items: '{{ ansible_prerequirements_packages }}'
+  register: command_res
+  changed_when: "'Es gibt nichts zu tun' not in command_res.stdout"