Try libvirt nsswitch with grep

roles/libvirt/tasks/main.yml

@@ -22,13 +22,9 @@
     groups: libvirt
 
 - name: Check if 'libvirt libvirt_guest' is in /etc/nsswitch.conf
-  become: true
-  lineinfile:
-    path: /etc/nsswitch.conf
-    line: libvirt libvirt_guest
-    state: present
-    check_mode: true
+  command: grep -c 'libvirt libvirt_guest' /etc/nsswitch.conf
   register: presence
+  changed_when: presence.stdout == '0'
 
 - name: Put 'libvirt libvirt_guest' in /etc/nsswitch.conf
   become: true
@@ -39,4 +35,4 @@
     state: present
     backrefs: true
     backup: true
-  when: presence.changed
+  when: presence.stdout == '0'