Fix class loader issue with LazyLoadingProxyInterceptor.

Restore original behaviour that was unintentionally changed by modifications related to #4148.

Closes: #4260
Original Pull Request: #4261

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/LazyLoadingProxyFactory.java

@@ -120,7 +120,7 @@ public final class LazyLoadingProxyFactory {
 		}
 
 		return prepareProxyFactory(propertyType,
-				() -> new LazyLoadingInterceptor(property, callback, source, exceptionTranslator)).getProxy();
+				() -> new LazyLoadingInterceptor(property, callback, source, exceptionTranslator)).getProxy(LazyLoadingProxy.class.getClassLoader());
 	}
 
 	/**