CompatHelper: bump compat for DiffEqCallbacks to 3, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the DiffEqCallbacks package from 2.25 to 2.25, 3.
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 89.45%. Comparing base (4bf61a0) to head (2de31ba).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1850      +/-   ##
==========================================
- Coverage   96.30%   89.45%   -6.85%     
==========================================
  Files         438      438              
  Lines       35577    35592      +15     
==========================================
- Hits        34259    31836    -2423     
- Misses       1318     3756    +2438     

Flag	Coverage Δ
unittests	89.45% <ø> (-6.85%)	⬇️

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[ranocha]

It's still using v2 of DiffEqCallbacks in the tests. We should check again later to see whether we can upgrade.