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

[github-actions[bot]]

This pull request changes the compat entry for the DiffEqCallbacks package from 2 to 2, 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.

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