putio: fix uploading to the wrong object on Update with overriden remote name

In this commit we discovered a problem with objects being uploaded to
the incorrect object name. It added an integration test for the
problem.

65b2e378e0 drive: fix incorrect remote after Update on object

This test was tripped by the putio backend and this patch fixes the
problem.

backend/putio/object.go

@@ -275,7 +275,7 @@ func (o *Object) Update(ctx context.Context, in io.Reader, src fs.ObjectInfo, op
 	if err != nil {
 		return err
 	}
-	newObj, err := o.fs.PutUnchecked(ctx, in, src, options...)
+	newObj, err := o.fs.putUnchecked(ctx, in, src, o.remote, options...)
 	if err != nil {
 		return err
 	}