fix(backend): `Retry-After`ヘッダーが実際には送信されなかった問題を修正 (#14597)

* move rate-limit-exceeded error reporting, earlier

a rate-limit-exceeded error has `kind:'client'`, so the branch that
adds the `Retry-After` would never get taken

(cherry picked from commit 8a982c61)

* Update Changelog

* fix

* indent

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Co-authored-by: dakkar <dakkar@thenautilus.net>