diff_objects shows "No changes" for deeply nested structures

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diff_objects can fail to show diffs in deeply nested structures due to truncation limits.

See marcoroth/minitest-difftastic#20 for details.

How max_depth (and I noticed max_items also) are handled when diffing via PrettyPlease should be fixed in this Gem, so that diffs are also shown for depper nested values and a different message than "No changes. is shown.

I concluded - also see the discussion in the linked ticket - that it is sufficient to provide a fix in this Gem and no adjustments in minitest-difftastic are needed.