Disable more @Bean method proxying

Previously, due to a quirk in Spring Framework, it was necessary to use bean method
proxying in @Configuration classes that define one or more FactoryBeans. This quirk has
now been addressed so this commit disables bean method proxying where it is now no longer
needed.

Closes gh-16533

spring-boot-project/spring-boot-test-autoconfigure/src/main/java/org/springframework/boot/test/autoconfigure/json/JsonTestersAutoConfiguration.java

@@ -75,7 +75,7 @@ public class JsonTestersAutoConfiguration {
 				null);
 	}
 
-	@Configuration
+	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(ObjectMapper.class)
 	static class JacksonJsonTestersConfiguration {
 
@@ -89,7 +89,7 @@ public class JsonTestersAutoConfiguration {
 
 	}
 
-	@Configuration
+	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(Gson.class)
 	static class GsonJsonTestersConfiguration {
 
@@ -102,7 +102,7 @@ public class JsonTestersAutoConfiguration {
 
 	}
 
-	@Configuration
+	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(Jsonb.class)
 	static class JsonbJsonTesterConfiguration {