fix(frontend): ユーザのサジェスト中に@を入力してもサジェスト結果が消えないように

[samunohito]

What

タイトルの通りです。
リモートユーザのサジェスト中に@が入力されると絞り込み結果が0件になってしまうのを解消しました。

Why

fix #14385

Additional info (optional)

実際に動作確認

Checklist

• 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

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 14.61%. Comparing base (495db27) to head (4adf77a).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/scripts/autocomplete.ts	0.00%	6 Missing ⚠️
...ackages/frontend/src/components/MkAutocomplete.vue	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #15435       +/-   ##
============================================
- Coverage    40.90%   14.61%   -26.29%     
============================================
  Files         1610      771      -839     
  Lines       162151    68626    -93525     
  Branches      3744     1234     -2510     
============================================
- Hits         66321    10029    -56292     
+ Misses       95355    58177    -37178     
+ Partials       475      420       -55     

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[mi-gh-maintainer]

Thank you 🙏