fix(test): remove stale etcd connection log assertions from TestWorkerNodeShutdownDuringTask

StartCleaner registers additional shutdown callbacks for task.cleanup and distribution
groups, producing extra log messages after "shutdown done". The etcd connection closing
messages now appear after those, outside the window captured in logs.String().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Matovidlo

internal/pkg/service/common/task/node_test.go

@@ -940,9 +940,6 @@ task/123/my-receiver/my-export/some.task/%s
 {"level":"info","message":"closing etcd session: context canceled","component":"task.etcd.session","node":"node1"}
 {"level":"info","message":"closed etcd session","component":"task.etcd.session","node":"node1"}
 {"level":"info","message":"shutdown done","component":"task","node":"node1"}
-{"level":"info","message":"closing etcd connection","component":"etcd.client"}
-{"level":"info","message":"closed etcd connection","component":"etcd.client"}
-{"level":"info","message":"exited"}
 `, logs.String())
 }