chore(test): longer streaming_upload_attempt_timeout_ms for backfill test only

[wcy-fdu]

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What's changed and what's your intention?

Previously we have located the root cause of Backfill Test failure in main cron: detail in apache/opendal#5101 (comment). We have a pr to increase the streaming_upload_attempt_timeout_ms from 10s to 20s and it indeed alleviated the issue, reducing the probability of failure.

However recently the same issue happened again several times, since the minio problem cannot be fixed in a short time, I suggest (maybe the only way) to continue to increase this timeout.

Close #18959

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