CompatHelper: bump compat for DiffEqCallbacks in [weakdeps] to 4, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the DiffEqCallbacks package from 2, 3 to 2, 3, 4.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.69%. Comparing base (1180100) to head (4a2dff6).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #753   +/-   ##
=======================================
  Coverage   99.69%   99.69%           
=======================================
  Files         123      123           
  Lines       11418    11418           
=======================================
  Hits        11383    11383           
  Misses         35       35           

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