bug: fix lock unlock position in worker goroutine spawning

[fufuok]

Follow up #374

Instead of adding this p.addRunning(1) and removing p.addRunning(-1) from all worker implementations. Can we just simply move p.lock.Unlock() underneath w.run()?

yes. great.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.16%. Comparing base (df029e6) to head (03342e0).
⚠️ Report is 14 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #376      +/-   ##
==========================================
+ Coverage   89.95%   94.16%   +4.21%     
==========================================
  Files          11       14       +3     
  Lines        1005      788     -217     
==========================================
- Hits          904      742     -162     
+ Misses         76       34      -42     
+ Partials       25       12      -13     

Flag	Coverage Δ
unittests	94.16% <100.00%> (+4.21%)	⬆️

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[panjf2000]

LGTM, thanks!