Merge branch '2.3.x' into 2.4.x

Closes gh-26317

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/SpringBootConfiguration.java

 /*
- * Copyright 2012-2019 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.
@@ -25,6 +25,7 @@ import java.lang.annotation.Target;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.annotation.AliasFor;
+import org.springframework.stereotype.Indexed;
 
 /**
  * Indicates that a class provides Spring Boot application
@@ -44,6 +45,7 @@ import org.springframework.core.annotation.AliasFor;
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 @Configuration
+@Indexed
 public @interface SpringBootConfiguration {
 
 	/**