fix(frontend): MkDateSeparatedListで月の違う同じ日はセパレータが出ないのを修正

[kakkokari-gtyih]

What

年・月・日すべてが同じかどうかを確かめるように

Why

Fix #909

Additional info (optional)

Checklist

• [x] Read the contribution guide
• [ ] Test working in a local environment
• [ ] (If needed) Add story of storybook
• [x] (If needed) Update CHANGELOG.md
• [ ] (If possible) Add tests

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 19.72%. Comparing base (837a8e1) to head (42ae654). Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...es/frontend/src/components/MkDateSeparatedList.vue	0.00%	13 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #14545 +/- ## =========================================== + Coverage 19.53% 19.72% +0.18% =========================================== Files 713 713 Lines 100287 100294 +7 Branches 997 995 -2 =========================================== + Hits 19591 19781 +190 + Misses 80152 79971 -181 + Partials 544 542 -2 ```

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[syuilo]

🙏🏿