Spring6-Scheduled-null

## Describe the bug

Spring 6 @Scheduled entpoint trace.

what i see in ui:
- 端点:SpringScheduled/null
- 跨度类型:Local
- 组件:SpringScheduled

Why `SpringScheduled/null` ?

## Steps to reproduce

kotlin: 2.0
spring-boot: 3.2.3
spring: 6.1.4
jdk: 21
skywalking: 9.1.0

sample code:

```kotlin
@Scheduled(fixedRate = 5, timeUnit = TimeUnit.SECONDS, scheduler = "myScheduler")
fun method1(){
...
}
```