Need support to diff with previous commit

## Please describe your suggestion: 提案の概要
Currently, this action is check diff between current commit with main branch

## Describe the solution you'd like: 考えうる解決方法
Support to check diff with previous commit like that
```
// to check diff between current commit with previous commit
git diff HEAD^ HEAD
```

## Describe alternatives you've considered: 考えうる代替案
## Additional context: 補足
