fix(backend): pagination with sinceId broken

[anatawa12]

What

#12564 (comment)

指摘の通り壊れていたので修正しました。

Why

Additional info (optional)

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: 6 lines in your changes are missing coverage. Please review.

Comparison is base (8866c53) 78.76% compared to head (d83bbf3) 78.79%.
Report is 3 commits behind head on develop.

Files	Patch %	Lines
.../backend/src/core/FanoutTimelineEndpointService.ts	75.00%	6 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #12586      +/-   ##
===========================================
+ Coverage    78.76%   78.79%   +0.03%     
===========================================
  Files          955      956       +1     
  Lines       103873   104054     +181     
  Branches      8337     8334       -3     
===========================================
+ Hits         81814    81991     +177     
- Misses       22059    22063       +4     

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[github-actions]

このPRによるapi.jsonの差分

差分はこちら

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[anatawa12]

@syuilo #12507 でsinceIdのpagenationを壊してしまったので修正したので確認していただけないでしょうか

[syuilo]

🙏