[EventHub] fix pylint error

Seeing the following pylint error in the azure-checkpointstoreblob-aio package:

INFO:root:Installed azure-eventhub-checkpointstoreblob-aio/azure_eventhub_checkpointstoreblob_aio-1.2.1a20250521001.tar.gz
pylint: commands[3]> python /mnt/vss/_work/1/s/eng/tox/run_pylint.py -t /mnt/vss/_work/1/s/sdk/eventhub/azure-eventhub-checkpointstoreblob-aio
************* Module azure.eventhub.extensions.checkpointstoreblobaio._blobstoragecsaio
azure/eventhub/extensions/checkpointstoreblobaio/_blobstoragecsaio.py:9: [C4763(do-not-import-asyncio), ] If asyncio.sleep() is being called and there is an azure core transport created, we should instead use the sleep function from the azure.core.pipeline.transport context instead of importing asyncio. For other imports of asyncio, ignore this warning.