Polish "Add test for beforeEach of OutputExtension"

See gh-33419

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/system/OutputExtensionExtendWithTests.java

@@ -17,7 +17,10 @@
 package org.springframework.boot.test.system;
 
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.extension.*;
+import org.junit.jupiter.api.extension.BeforeAllCallback;
+import org.junit.jupiter.api.extension.BeforeEachCallback;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.junit.jupiter.api.extension.ExtensionContext;
 
 import static org.assertj.core.api.Assertions.assertThat;