fix(功能用例xmind导入): 修复xmind导入功能用例时id于用例在xmind的顺序不符，为倒序ID的问题

--bug=1008530 --user=宋天阳
【github#6867】通过XMIND导入用例时，生成的用例ID与实际XMIND编排的用例顺序不符，为倒序ID，请修改
https://www.tapd.cn/55049933/s/1078804

backend/src/main/java/io/metersphere/track/service/TestCaseService.java

@@ -662,7 +662,7 @@ public class TestCaseService {
                 testcase.setUpdateTime(System.currentTimeMillis());
                 testcase.setNodeId(nodePathMap.get(testcase.getNodePath()));
                 testcase.setSort(sort.getAndIncrement());
-                int number = num.decrementAndGet();
+                int number = num.incrementAndGet();
                 testcase.setNum(number);
                 if (project.getCustomNum() && StringUtils.isBlank(testcase.getCustomNum())) {
                     testcase.setCustomNum(String.valueOf(number));