Cloud Storage S3 ignores custom endpoint when using prefix

I have an object storage at scaleway and try to use it as source storage in LS. The custom endpoint for my bucket is something like `https://bucketname.s3.nl-ams.scw.cloud`. While probing for the correct credentials, I filled the `Bucket Prefix` field and suddently LS reports the error, that it could not connect to the endpoint `https://s3.nl-ams.amazonaws.com/bucketname?list-type=2&prefix=Test&max-keys=1&encoding-type=url`

Steps to reproduce the behavior:
1. Add Source Storage
2. Choose AWS S3
3. Fill in bucket name, Bucket Prefix and custom S3 Endpoint
4. See error

Regardless of whether my own S3 service supports the prefix, the custom endpoint should be taken into account.

- OS: Ubuntu
- Label Studio Version 1.7.2