Fix some ansible-lint complaints.

roles/low-power/tasks/main.yml

@@ -1,5 +1,5 @@
 - name: install some packages
-  apt: name={{ item }} state=latest
+  apt: name={{ item }} state=latest # noqa package-latest
   with_items:
     - powertop
 
@@ -7,9 +7,11 @@
   copy:
     src: powertop.service
     dest: /etc/systemd/system/powertop.service
+    mode: 0644
 
 - name: install powertop.timer
   copy:
     src: powertop.timer
     dest: /etc/systemd/system/powertop.timer
+    mode: 0644
   notify: enable powertop timer