Synchronize access to ArrayList in prose test

This prevents the occasional ConcurrentModificationException during
test runs.

JAVA-3626

Author: jyemin

driver-sync/src/test/functional/com/mongodb/client/ServerDiscoveryAndMonitoringProseTests.java

@@ -36,6 +36,7 @@
 import static com.mongodb.ClusterFixture.isStandalone;
 import static com.mongodb.ClusterFixture.serverVersionAtLeast;
 import static com.mongodb.client.Fixture.getMongoClientSettingsBuilder;
+import static java.util.Collections.synchronizedList;
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import static org.bson.BsonDocument.parse;
 import static org.junit.Assert.assertFalse;
@@ -73,7 +74,7 @@ public void testRTTUpdates() throws InterruptedException {
         assumeTrue(isStandalone());
         assumeTrue(serverVersionAtLeast(4, 4));
 
-        List<ServerDescriptionChangedEvent> events = new ArrayList<>();
+        List<ServerDescriptionChangedEvent> events = synchronizedList(new ArrayList<>());
         MongoClientSettings settings = getMongoClientSettingsBuilder()
                                        .applicationName("streamingRttTest")
                                        .applyToServerSettings(new Block<ServerSettings.Builder>() {