fix(misskey-js): wrong hashtag channel param type

[zyoshoka]

What

misskey-js で hashtag チャンネルに接続する際の引数の型がおかしいのを修正します。

Why

引数にただの文字列を指定（もしくは省略）するのでは正しく動作しませんので https://github.com/misskey-dev/misskey/blob/76b9bc478ae6c18fb1f1c9c0f290e6c13493c16b/packages/backend/src/server/api/stream/channels/hashtag.ts#L32-L34

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

[codecov[bot]]

Codecov Report

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

Project coverage is 41.36%. Comparing base (f93a575) to head (e5833af). Report is 2 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #14611 +/- ## =========================================== + Coverage 39.73% 41.36% +1.63% =========================================== Files 1539 1543 +4 Lines 192271 198008 +5737 Branches 3479 2499 -980 =========================================== + Hits 76401 81914 +5513 - Misses 115278 115532 +254 + Partials 592 562 -30 ```

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[syuilo]

🙏🏻