Bodgy-hack: force Test::Differences to behave.

Test::Differences, given a hash of scalars, uses the stupid, nasty, unhelpful
flatten style, which is SHIT.

See: https://rt.cpan.org/Public/Bug/Display.html?id=95446

I may have tie @DrHyde's beard to a chair tomorrow and refuse to release him
unless he fixes that nastyness so this horrific bodge can be reverted.