During S3 backup, errors may occur if there is "/" at the end of the endpoint

[tongtongyin]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

when S3 backup or restore, If "/" is added last in the endpoint, an error may occur

2. What did you expect to see?

Whether "/" is added last, the backup can be successful

3. What did you see instead?

4. What version of BR and TiDB/TiKV/PD are you using?

br -4.0.11
br -5
The above problem occurs only when there is data in instance. Therefore, when br version is 4.0.11, this problem will not occur when backing up empty instances, because the system library will not be backed up; However, when the br version is 5, even for empty instances, Br the system library will be backed up during backup.

5. Operation logs

   • Please upload br.log for BR if possible
   • Please upload tidb-lightning.log for TiDB-Lightning if possible
   • Please upload tikv-importer.log from TiKV-Importer if possible
   • Other interesting logs

6. Configuration of the cluster and the task

   • tidb-lightning.toml for TiDB-Lightning if possible
   • tikv-importer.toml for TiKV-Importer if possible
   • topology.yml if deployed by TiUP

7. Screenshot/exported-PDF of Grafana dashboard or metrics' graph in Prometheus if possible

[kennytm]

duplicate of #30104

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.