build(webhook): package for nodenext es6 with minimum node20 test

[zimeg]

Summary

WIP for #2359!

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

❌ Patch coverage is 98.14815% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.96%. Comparing base (ff03f78) to head (56a6183).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2393      +/-   ##
==========================================
- Coverage   93.01%   92.96%   -0.06%     
==========================================
  Files          40       42       +2     
  Lines       11112    11169      +57     
  Branches      713      691      -22     
==========================================
+ Hits        10336    10383      +47     
- Misses        764      774      +10     
  Partials       12       12              

Flag	Coverage Δ
cli-hooks	95.23% <ø> (ø)
cli-test	94.80% <ø> (ø)
oauth	77.39% <ø> (ø)
socket-mode	61.87% <ø> (ø)
web-api	98.07% <ø> (ø)
webhook	93.93% <98.14%> (-2.73%)	⬇️

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