Fix assertions in LoggerMessageFactoryCustomizationTest

Author: ppkarwasz

log4j-core-test/src/test/java/org/apache/logging/log4j/core/LoggerMessageFactoryCustomizationTest.java

@@ -60,8 +60,8 @@ private static void assertTestMessageFactories(
             Logger logger,
             Class<? extends MessageFactory> messageFactoryClass,
             Class<? extends FlowMessageFactory> flowMessageFactoryClass) {
-        assertThat((MessageFactory) logger.getMessageFactory()).isInstanceOf(messageFactoryClass);
-        assertThat(logger.getFlowMessageFactory()).isInstanceOf(flowMessageFactoryClass);
+        assertThat(logger.getMessageFactory().getClass()).isEqualTo(messageFactoryClass);
+        assertThat(logger.getFlowMessageFactory().getClass()).isEqualTo(flowMessageFactoryClass);
     }
 
     public static class TestMessageFactory extends AbstractMessageFactory {