Fix session leak in PeersV2NodeRefreshIT test

PeersV2NodeRefreshIT#should_successfully_send_peers_v2_node_refresh_query integration
test does not close its test session, leading to leaks when integration
tests suite is executed in CI. This affects
SessionLeakIT#should_warn_when_session_count_exceeds_threshold test, which sees the
leaked session and fails due to an unexpected number of active sessions.

The change adds post-test cleanup in PeersV2NodeRefreshIT to ensure that session
is properly closed after the test, preventing it from affecting subsequent tests.

Author: dimakr

Diff for: integration-tests/src/test/java/com/datastax/oss/driver/core/PeersV2NodeRefreshIT.java

@@ -27,6 +27,7 @@
 import com.datastax.oss.simulacron.server.BoundCluster;
 import com.datastax.oss.simulacron.server.Server;
 import java.util.concurrent.ExecutionException;
+import org.junit.After;
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.junit.Test;
@@ -36,6 +37,7 @@ public class PeersV2NodeRefreshIT {
 
   private static Server peersV2Server;
   private static BoundCluster cluster;
+  private static CqlSession session;
 
   @BeforeClass
   public static void setup() {
@@ -53,11 +55,17 @@ public static void tearDown() {
     }
   }
 
+  @After
+  public void closeSession() {
+    if (session != null) {
+      session.close();
+    }
+  }
+
   @Test
   public void should_successfully_send_peers_v2_node_refresh_query()
       throws InterruptedException, ExecutionException {
-    CqlSession session =
-        CqlSession.builder().addContactPoint(cluster.node(1).inetSocketAddress()).build();
+    session = CqlSession.builder().addContactPoint(cluster.node(1).inetSocketAddress()).build();
     Node node = findNonControlNode(session);
     ((InternalDriverContext) session.getContext())
         .getMetadataManager()