[PR #8608/c4acabc backport][3.10] Fix timer handle churn in websocket heartbeat

[bdraco]

Co-authored-by: Sam Bull git@sambull.org
(cherry picked from commit c4acabc)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.66%. Comparing base (72f41aa) to head (b92861f).
Report is 205 commits behind head on 3.10.

Additional details and impacted files

@@            Coverage Diff             @@
##             3.10    #8639      +/-   ##
==========================================
+ Coverage   97.63%   97.66%   +0.03%     
==========================================
  Files         108      108              
  Lines       33698    33852     +154     
  Branches     4016     4027      +11     
==========================================
+ Hits        32902    33063     +161     
+ Misses        591      588       -3     
+ Partials      205      201       -4     

Flag	Coverage Δ
CI-GHA	97.58% <100.00%> (+0.03%)	⬆️
OS-Linux	97.25% <100.00%> (+0.03%)	⬆️
OS-Windows	94.76% <100.00%> (+0.01%)	⬆️
OS-macOS	96.92% <98.55%> (+0.02%)	⬆️
Py-3.10.11	97.03% <98.55%> (+0.02%)	⬆️
Py-3.10.14	96.98% <100.00%> (+0.03%)	⬆️
Py-3.11.9	97.21% <100.00%> (+0.03%)	⬆️
Py-3.12.4	97.33% <100.00%> (+0.03%)	⬆️
Py-3.8.10	94.50% <100.00%> (+0.01%)	⬆️
Py-3.8.18	96.88% <100.00%> (+0.03%)	⬆️
Py-3.9.13	97.03% <98.55%> (+0.02%)	⬆️
Py-3.9.19	96.99% <100.00%> (+0.03%)	⬆️
Py-pypy7.3.16	96.57% <100.00%> (+0.03%)	⬆️
VM-macos	96.92% <98.55%> (+0.02%)	⬆️
VM-ubuntu	97.25% <100.00%> (+0.03%)	⬆️
VM-windows	94.76% <100.00%> (+0.01%)	⬆️

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