Avoid bean override with CachingMetadataReaderFactoryPostProcessor

Closes gh-28705

Author: snicoll

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/SharedMetadataReaderFactoryContextInitializer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -99,10 +99,12 @@ public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) t
 		}
 
 		private void register(BeanDefinitionRegistry registry) {
-			BeanDefinition definition = BeanDefinitionBuilder
-					.genericBeanDefinition(SharedMetadataReaderFactoryBean.class, SharedMetadataReaderFactoryBean::new)
-					.getBeanDefinition();
-			registry.registerBeanDefinition(BEAN_NAME, definition);
+			if (!registry.containsBeanDefinition(BEAN_NAME)) {
+				BeanDefinition definition = BeanDefinitionBuilder
+						.rootBeanDefinition(SharedMetadataReaderFactoryBean.class, SharedMetadataReaderFactoryBean::new)
+						.getBeanDefinition();
+				registry.registerBeanDefinition(BEAN_NAME, definition);
+			}
 		}
 
 		private void configureConfigurationClassPostProcessor(BeanDefinitionRegistry registry) {