c/partition_balancer: don't finish rebalance if some ntps are immutable

Previously, we finished counts rebalance if no new moves could be
found, even when some partitions were not moveable. This could lead to
finishing too early and not achieving balanced distribution when many
partitions were not moveable (e.g. because they are disabled due to
recovery mode).

src/v/cluster/partition_balancer_planner.cc

@@ -1953,6 +1953,10 @@ ss::future<> partition_balancer_planner::get_counts_rebalancing_actions(
                     }
                 }
             },
+            [&](immutable_partition& p) {
+                p.report_failure(change_reason::partition_count_rebalancing);
+                should_stop = false;
+            },
             [](auto&) {});
 
           return ss::stop_iteration::no;