bisync: fix output capture restoring the wrong output for logrus

Before this change, if rclone is used as a library and logrus is used
after a call to rc `sync/bisync`, logging does not work anymore and
leads to writing to a closed pipe.

This change restores the output correctly.

Fixes rclone#8158

cmd/bisync/bilib/output.go

@@ -5,20 +5,13 @@ import (
 	"bytes"
 	"log"
 
-	"github.com/rclone/rclone/fs"
 	"github.com/sirupsen/logrus"
 )
 
 // CaptureOutput runs a function capturing its output.
 func CaptureOutput(fun func()) []byte {
 	logSave := log.Writer()
-	logrusSave := logrus.StandardLogger().Writer()
-	defer func() {
-		err := logrusSave.Close()
-		if err != nil {
-			fs.Errorf(nil, "error closing logrusSave: %v", err)
-		}
-	}()
+	logrusSave := logrus.StandardLogger().Out
 	buf := &bytes.Buffer{}
 	log.SetOutput(buf)
 	logrus.SetOutput(buf)