fix(misskey-js): content-typeはapplication/jsonでないもののみを記録するように

[kakkokari-gtyih]

What

• content-typeはapplication/jsonでないもののみを記録するように
• content-type が判別できない場合はapplication/jsonをデフォルトにするように

Why

• サイズ削減
• Fix misskey-js: fallback to Content-Type: application/json for unknown endpoints #14502

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

All modified and coverable lines are covered by tests ✅

Project coverage is 41.57%. Comparing base (3fe7e37) to head (f02f28b).
Report is 6 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #14508       +/-   ##
============================================
+ Coverage    20.17%   41.57%   +21.39%     
============================================
  Files          725     1551      +826     
  Lines       100502   196640    +96138     
  Branches      1045     2737     +1692     
============================================
+ Hits         20279    81750    +61471     
- Misses       79681   114328    +34647     
- Partials       542      562       +20     

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[syuilo]

🙏🏿