Fix bug that worker doesn't return after context cancel

[hongkuancn]

I think we also need to return immediately in the inner context.Done(), otherwise it is possible to loop all the time. According to https://stackoverflow.com/a/51296312, it also returns immediately.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.35%. Comparing base (5f162d4) to head (1b21aaa).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
worker.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #71      +/-   ##
==========================================
- Coverage   99.00%   98.35%   -0.66%     
==========================================
  Files           4        4              
  Lines         302      304       +2     
==========================================
  Hits          299      299              
- Misses          3        5       +2     

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[alitto]

Thank you!