fix: ensure the dokku-retire timer is properly installed

Closes #3615

plugins/scheduler-docker-local/install

@@ -38,9 +38,15 @@ Description=Run dokku-retire.service every 5 minutes
 
 [Timer]
 OnCalendar=*:0/5
+Persistent=true
+
+[Install]
+WantedBy=timers.target
 EOF
     if command -v systemctl &>/dev/null; then
       systemctl --quiet reenable dokku-retire
+      systemctl --quiet enable dokku-retire.timer
+      systemctl --quiet start dokku-retire.timer
     fi
   else
     cat <<EOF >/etc/cron.d/dokku-retire

tests/unit/30_scheduler-docker-local.bats

@@ -0,0 +1,18 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+setup() {
+  global_setup
+}
+
+teardown() {
+  global_teardown
+}
+
+@test "(scheduler-docker-local) timer installed" {
+  run /bin/bash -c "systemctl list-timers | grep dokku-retire"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+}