Fix memory error on shutdown (PHP-8.1)

[twose]

Ref of function_name was held by zend_fcall_info_init().

[codecov]

Codecov Report

Merging #4325 (e16ce83) into master (db6deb0) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4325      +/-   ##
==========================================
- Coverage   50.73%   50.68%   -0.05%     
==========================================
  Files          72       72              
  Lines       14516    14516              
==========================================
- Hits         7364     7358       -6     
- Misses       7152     7158       +6     

Impacted Files	Coverage Δ
src/os/async_thread.cc	68.85% <0.00%> (-1.32%)	⬇️
src/server/reactor_thread.cc	55.80% <0.00%> (-0.35%)	⬇️
src/server/port.cc	50.00% <0.00%> (-0.28%)	⬇️

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