docs: Reformulate deprecation notice for Commits field in PushEvent

[jizi]

Fixes #3872

[gmlewis]

Thank you, @jizi!
LGTM.
Merging.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.48%. Comparing base (07ddcd9) to head (4791280).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3880   +/-   ##
=======================================
  Coverage   92.48%   92.48%           
=======================================
  Files         200      200           
  Lines       14564    14564           
=======================================
  Hits        13469    13469           
  Misses        895      895           
  Partials      200      200           

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