使用application.yml配置dubbo时出错

当配置文件采用yml格式的时候，base-packages是一个Set，所以会自动补全成这样的形式，但是服务并没有被扫描到
```yaml
dubbo:
scan:
base-packages:
- io.example.test.service
```

采用这种写法就可以正常工作：
```yaml
dubbo:
scan:
base-packages: io.example.test.service
```

demo是这里面的https://github.com/apache/dubbo-spring-boot-project/blob/master/README_CN.md
把application.properties换成application.yml之后就有问题了

Start with the demo and configuration examples in README_CN.md, comparing application.properties with application.yml and the two base-packages forms shown in the issue. Trace how the YAML value reaches Dubbo's scan configuration, then verify that the list form scans the service while the existing scalar form continues to work.

Written by the indexing model from the issue text.