Add junit5 test code for module [linkis-variable]

### Add junit5 test code for module [linkis-variable]
- Module: linkis-variable
- Location:linkis-public-enhancements/linkis-variable
- Task status:✗(unfinished)/ ✓(finished)
- Test code guide:https://linkis.apache.org/zh-CN/community/how-to-write-unit-test-code/
- Test code example: https://github.com/apache/incubator-linkis/tree/master/linkis-public-enhancements/linkis-publicservice/linkis-jobhistory/src/test
---
- 模块名: linkis-variable
- 代码位置:linkis-public-enhancements/linkis-variable
- 任务状态:✗(unfinished)/ ✓(finished)
- 单测编写指引:https://linkis.apache.org/zh-CN/community/how-to-write-unit-test-code/
- 参考样例: https://github.com/apache/incubator-linkis/tree/master/linkis-public-enhancements/linkis-publicservice/linkis-jobhistory/src/test

| Task status| Class | Type| Level of Difficulty | Note |
| :------ | :------ | :------: | :------: | :------: |
| ✓ |org.apache.linkis.variable.dao.*| Builder | normal | |
| ✓ | org.apache.linkis.variable.service.*| service | normal | |
| ✓ |org.apache.linkis.variable.restful.api.VariableRestfulApi| service | normal | |
| ✗ |org.apache.linkis.variable.exception.VariableException| exception | normal | |
| ✗ |org.apache.linkis.variable.util.Constants| util | normal | |