简化 dict data 的单元测试，将新增、修改、删除涉及的公用方法，单独测试

src/main/java/cn/iocoder/dashboard/modules/system/dal/mysql/dict/SysDictDataMapper.java

@@ -15,13 +15,13 @@ import java.util.List;
 @Mapper
 public interface SysDictDataMapper extends BaseMapperX<SysDictDataDO> {
 
-    default SysDictDataDO selectByDictTypeAndLabel(String dictType, String value) {
+    default SysDictDataDO selectByDictTypeAndValue(String dictType, String value) {
         return selectOne(new QueryWrapper<SysDictDataDO>().eq("dict_type", dictType)
                 .eq("value", value));
     }
 
     default int selectCountByDictType(String dictType) {
-        return selectCount(new QueryWrapper<SysDictDataDO>().eq("dict_type", dictType));
+        return selectCount("dict_type", dictType);
     }
 
     default PageResult<SysDictDataDO> selectPage(SysDictDataPageReqVO reqVO) {