Fix timer channel drain to avoid hanging in Go 1.23

[dany74q]

• Fix timer channel drain to avoid hanging in go1.23 w/ asynctimerchan=0 (Go 1.23 timer changes can lead to hangs #5868)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.5%. Comparing base (e500945) to head (46558ff).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5869     +/-   ##
=======================================
- Coverage   84.5%   84.5%   -0.1%     
=======================================
  Files        272     272             
  Lines      22734   22736      +2     
=======================================
+ Hits       19225   19226      +1     
- Misses      3166    3167      +1     
  Partials     343     343             

see 2 files with indirect coverage changes

[pellared]

This fix is no longer needed since Go 1.23.2 thanks to fixing golang/go#69312.

Credits: @ash2k