Make inner classes static when feasible (on main)

A static nested class does not keep an implicit reference to its
enclosing instance.

This prevents a common cause of memory leaks and uses less memory per
instance of the class.

Closes gh-28433

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassPostProcessor.java

@@ -509,7 +509,7 @@ public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPo
 	}
 
 
-	private class AotContribution implements BeanFactoryInitializationAotContribution {
+	private static class AotContribution implements BeanFactoryInitializationAotContribution {
 
 		private static final String BEAN_FACTORY_VARIABLE = BeanFactoryInitializationCode.BEAN_FACTORY_VARIABLE;