fix(frontend): データセーバーを有効にしているときにメンションのアイコンがアニメーションしないように

[KisaragiEffective]

What

MkMentionのアニメーションしない条件をMkAvatarと揃える。 close #14663

Why

MkAvatarと一貫性がない・従量課金性回線でアニメーション画像が読み込まれるとクォータに優しくない

Additional info (optional)

Checklist

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

[syuilo]

🙏🏻

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 19.58%. Comparing base (1074d62) to head (a94fcd0). Report is 4 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #14674 +/- ## ============================================ - Coverage 39.71% 19.58% -20.13% ============================================ Files 1545 716 -829 Lines 193812 101543 -92269 Branches 3592 986 -2606 ============================================ - Hits 76977 19890 -57087 + Misses 116239 81108 -35131 + Partials 596 545 -51 ```

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