Competitive-verifier

- Check file existence in prev result

- Fix need_verification
- Fix merge logic

- log.group of git.get_commit_time

- Remove GitHub Actions output `verify-result`
- Show verify result
- Allow skip result

What's Changed
* Add `fetch-depth: 0` to docs-and-check by kzrnm in https://github.com/competitive-verifier/competitive-verifier/pull/77
* [oj-resolve][C++] インクルードガードの前の空行やコメント行を許容する by kzrnm in https://github.com/competitive-verifier/competitive-verifier/pull/80
* encoding を判定する by kzrnm in https://github.com/competitive-verifier/competitive-verifier/pull/83



**Full Changelog**: https://github.com/competitive-verifier/competitive-verifier/compare/v1.2.0...v1.2.1

What's Changed
* Add `fetch-depth: 0` to docs-and-check by kzrnm in https://github.com/competitive-verifier/competitive-verifier/pull/77
* [oj-resolve][C++] インクルードガードの前の空行やコメント行を許容する by kzrnm in https://github.com/competitive-verifier/competitive-verifier/pull/79
* [oj-resolve][C++] インクルードガードの前の空行やコメント行を許容する by kzrnm in https://github.com/competitive-verifier/competitive-verifier/pull/80
* encoding を判定する by kzrnm in https://github.com/competitive-verifier/competitive-verifier/pull/83


**Full Changelog**: https://github.com/competitive-verifier/competitive-verifier/compare/v1.1.0...v1.2.1-dev