Config in application.properties but still tried to load dubbo.properties

I tried to switch from the traditional Dubbo config `dubbo.properties` to dubbo-spring-boot-start and config dubbo config in application.properties. But after I delete my dubbo.properties configuration file. I cannot start the application.

```
2021-01-08 21:00:45,019 WARN org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplication
Context [main] Exception encountered during context initialization - cancelling refresh attempt: org.springframework.
beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [Pla
tformAdminServer]; nested exception is java.io.FileNotFoundException: class path resource [dubbo.properties] cannot b
e opened because it does not exist
2021-01-08 21:00:45,029 ERROR org.springframework.boot.SpringApplication [main] Application run failed
org.springframework.beans.factory.BeanDefinitionStoreException: Failed to parse configuration class [PlatformAdminServer]; nested exception is java.io.FileNotFoundException: class path resource [dubbo.
properties] cannot be opened because it does not exist
at org.springframework.context.annotation.ConfigurationClassParser.parse(ConfigurationClassParser.java:188)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(Config
urationClassPostProcessor.java:319)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(C
onfigurationClassPostProcessor.java:236)
```

I have the dependency.

```

org.apache.dubbo
dubbo-spring-boot-starter
2.7.8

org.apache.dubbo
dubbo
2.7.8



org.mybatis.spring.boot
mybatis-spring-boot-starter

```

With Spring Boot version 2.3.2.RELEASE.

Start by reproducing the startup failure with Spring Boot 2.3.2.RELEASE and the listed Dubbo 2.7.8 dependencies, then trace the reported missing dubbo.properties resource during application initialization. Done means the application starts using configuration from application.properties after dubbo.properties is removed.

Written by the indexing model from the issue text.