[borgbackup_client] fix risky file permission on apt config for pinning version

roles/borgbackup_client/tasks/main.yml

@@ -3,6 +3,9 @@
   template:
     src: "apt/{{ item }}.j2"
     dest: "/etc/apt/{{ item }}"
+    owner: root
+    group: root
+    mode: u=rw,g=r,o=
   loop:
     - sources.list.d/bullseye.list
     - preferences.d/borgmatic-bullseye