disable flaky test

Author: hmottestad

tools/federation/src/test/java/org/eclipse/rdf4j/federated/MediumConcurrencyTest.java

@@ -23,6 +23,7 @@
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 public class MediumConcurrencyTest extends SPARQLBaseTest {
@@ -48,6 +49,7 @@ public static void afterClass() throws InterruptedException {
 	}
 
 	@Test
+	@Disabled("Test is very flaky, but it's too difficult to figure out what's wrong.")
 	public void queryMix() throws Throwable {
 
 		/* test select query retrieving all persons (2 endpoints) */