tests/maintenance_test: increase the number of partitions

Previously when this test was running in CI there were not a lot of partitions (12)
and the leadership balancer could mute them all after several ticks (it mutes the
partitions that it moves). After that it cannot take any further action for some time
and the node that comes out of the maintenance mode won't acquire any new leaders.

Increase the number of partitions in the test to avoid that.

Fixes: redpanda-data#13650

tests/rptest/tests/maintenance_test.py

@@ -29,9 +29,9 @@ def __init__(self, *args, **kwargs):
         # Vary partition count relative to num_cpus. This is to ensure that
         # leadership is moved back to a node that exits maintenance.
         num_cpus = self.redpanda.get_node_cpu_count()
-        self.topics = (TopicSpec(partition_count=num_cpus * 3,
+        self.topics = (TopicSpec(partition_count=num_cpus * 5,
                                  replication_factor=3),
-                       TopicSpec(partition_count=num_cpus * 3,
+                       TopicSpec(partition_count=num_cpus * 10,
                                  replication_factor=3))
         self.admin = Admin(self.redpanda)
         self.rpk = RpkTool(self.redpanda)