Fix: 修复 DataclassEncoder 嵌套 encode 的问题

[AkiraXie]

No description provided.

[codecov]

Codecov Report

Merging #812 (1d6a333) into master (9dd989c) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #812      +/-   ##
==========================================
+ Coverage   76.41%   76.47%   +0.06%     
==========================================
  Files          42       42              
  Lines        3061     3061              
==========================================
+ Hits         2339     2341       +2     
+ Misses        722      720       -2     

Flag	Coverage Δ
unittests	76.47% <100.00%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
nonebot/utils.py	86.25% <100.00%> (+2.50%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9dd989c...1d6a333. Read the comment docs.

[github-actions]

🚀 Deployed on https://deploy-preview-812--nonebot2.netlify.app