test/cluster: fix flaky test_cleanup_stop by using asyncio.sleep

The test was using time.sleep(1) (a blocking call) to wait after
scheduling the stop_compaction task, intending to let it register on
the server before releasing the sstable_cleanup_wait injection point.

However, time.sleep() blocks the asyncio event loop entirely, so the
asyncio.create_task(stop_compaction) task never gets to run during the
sleep. After the sleep, the directly-awaited message_injection() runs
first, releasing the injection point before stop_compaction is even
sent. By the time stop_compaction reaches Scylla, the cleanup has
already completed successfully -- no exception is raised and the test
fails.

Fix by replacing time.sleep(1) with await asyncio.sleep(1), which
yields control to the event loop and allows the stop_compaction task
to actually send its HTTP request before message_injection is called.

Fixes: SCYLLADB-834

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Closes scylladb/scylladb#29202

test/cluster/test_sstable_cleanup_stop.py

@@ -11,7 +11,6 @@ from test.cluster.util import check_token_ring_and_group0_consistency, new_test_
 import pytest
 import asyncio
 import logging
-import time
 
 logger = logging.getLogger(__name__)
 @pytest.mark.asyncio
@@ -53,7 +52,7 @@ async def test_cleanup_stop(manager: ManagerClient):
         await s0_log.wait_for('sstable_cleanup_wait: waiting', from_mark=s0_mark)
 
         stop_cleanup = asyncio.create_task(manager.api.stop_compaction(servers[0].ip_addr, "CLEANUP"))
-        time.sleep(1)
+        await asyncio.sleep(1)
 
         await manager.api.message_injection(servers[0].ip_addr, "sstable_cleanup_wait")
         await stop_cleanup