Fix logger refactoring regression: manager logging add (#24847)

The `rotate` option is optional.

Test result:

![image](https://github.com/go-gitea/gitea/assets/2114189/7cff8207-dcf3-4988-adef-247f1c9316e7)

routers/private/manager.go

@@ -155,7 +155,7 @@ func AddLogger(ctx *context.PrivateContext) {
 		writerOption := log.WriterFileOption{}
 		fileName, _ := opts.Config["filename"].(string)
 		writerOption.FileName = setting.LogPrepareFilenameForWriter(fileName, opts.Writer+".log")
-		writerOption.LogRotate = opts.Config["rotate"].(bool)
+		writerOption.LogRotate, _ = opts.Config["rotate"].(bool)
 		maxSizeShift, _ := opts.Config["maxsize"].(int)
 		if maxSizeShift == 0 {
 			maxSizeShift = 28