fix ansible_lint issues

Use prefix for role variables, have an ending newline at the end of
files and use changed_when for command.
Also exclude *.sops.yaml files from ansible-lint.

roles/docker_compose/defaults/main.yaml

@@ -1,2 +1,2 @@
 docker_compose__configuration_files: [ ]
-docker_compose__restart_cmd: ""
+docker_compose__restart_cmd: ""

roles/docker_compose/handlers/main.yaml

@@ -9,4 +9,5 @@
     cmd: /usr/bin/docker compose {{ docker_compose__restart_cmd }}
     chdir: /ansible_docker_compose
   become: true
+  changed_when: true  # Mark this as always changed (for now?).
   when: docker_compose__restart_cmd != ""