Fix Checkstyle violation

Author: sbrannen

spring-web/src/test/java/org/springframework/http/server/reactive/ErrorHandlerIntegrationTests.java

@@ -18,7 +18,6 @@
 
 import java.net.URI;
 
-import org.junit.Assume;
 import org.junit.jupiter.api.Assumptions;
 import reactor.core.publisher.Mono;