s3 RequestCanceled should be taken as graceful shutdown too

[D3Hunter]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

on graceful shutdown, err might returns from s3:

https://github.com/aws/aws-sdk-go/blob/9d1f49ba63bdac44a5b9f4d736e79d792e389e8a/aws/credentials/credentials.go#L246-L249

[2023/11/15 19:28:53.387 +08:00] [WARN] [s3.go:890] ["open new s3 reader failed"] [file=.....sysbench.user_data1.000001539.csv] [error="RequestCanceled: request context canceled\ncaused by: context canceled"]

2. What did you expect to see? (Required)

task keeps run

3. What did you see instead (Required)

failed

4. What is your TiDB version? (Required)

master