Fix cluster hostnames test causing failover while running valgrind (#10991)

In the newly added cluster hostnames test, the primary is failing over during the reboot
for valgrind so we are validating the wrong node. This change just sets the replica to
prevent taking over, which seems to fix the test.

We could have also set the timeout higher, but it slows down the test.

tests/unit/cluster/hostnames.tcl

@@ -203,8 +203,14 @@ test "Verify the nodes configured with prefer hostname only show hostname for ne
 test "Test restart will keep hostname information" {
     # Set a new hostname, reboot and make sure it sticks
     R 0 config set cluster-announce-hostname "restart-1.com"
+    
     # Store the hostname in the config
     R 0 config rewrite
+
+    # If the primary is slow to reboot it might get demoted, so prevent the replica
+    # from nominating itself.
+    R 3 config set cluster-replica-no-failover yes
+
     restart_server 0 true false
     set slot_result [R 0 CLUSTER SLOTS]
     assert_equal [lindex [get_slot_field $slot_result 0 2 3] 1] "restart-1.com"