fix: build failures with older cython 0.29 series

[bdraco]

fixes #1230

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (3e89294) 99.82% compared to head (b28ea92) 99.82%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1232   +/-   ##
=======================================
  Coverage   99.82%   99.82%           
=======================================
  Files          25       25           
  Lines        2790     2791    +1     
  Branches      479      479           
=======================================
+ Hits         2785     2786    +1     
  Misses          3        3           
  Partials        2        2           

Files Changed	Coverage Δ
src/zeroconf/__init__.py	100.00% <100.00%> (ø)
src/zeroconf/_services/registry.py	100.00% <100.00%> (ø)

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