fix(测试计划): 修复英文下标签未匹配问题

backend/framework/sdk/src/main/resources/i18n/case_en_US.properties

@@ -272,7 +272,7 @@ download_template_failed=Download template failed
 functional_case=Functional case
 xmind_prerequisite=Prerequisite
 xmind_description=Remark
-xmind_tags=tags
+xmind_tags=Tag
 xmind_textDescription=Text description
 xmind_expectedResult=Expected result
 xmind_step=Step

backend/services/case-management/src/main/java/io/metersphere/functional/service/FunctionalCaseFileService.java

@@ -864,7 +864,7 @@ public class FunctionalCaseFileService {
             String content = matcher.group(1);
             return content;
         }
-        return StringUtils.EMPTY;
+        return html;
     }