cmd serve s3: fix ListObjectsV2 response

add trailing slash to s3 ListObjectsV2 response because some clients expect a trailing forward slash to distinguish if the returned object is a directory

Fixes #8464

cmd/serve/s3/list.go

@@ -28,7 +28,8 @@ func (b *s3Backend) entryListR(_vfs *vfs.VFS, bucket, fdPath, name string, addPr
 
 		if entry.IsDir() {
 			if addPrefix {
-				response.AddPrefix(objectPath)
+				prefixWithTrailingSlash := objectPath + "/"
+				response.AddPrefix(prefixWithTrailingSlash)
 				continue
 			}
 			err := b.entryListR(_vfs, bucket, path.Join(fdPath, object), "", false, response)