Adds checks for nested data structures not of the same type as the outermost structure.

[ptkenny]

head-fork: ptkenny/pytest compare: ptk/approx-nested-fix

base-fork: pytest-dev/pytest base: main

Closes #10210.

Apparently there is some ongoing design discussion related to this bug that I'm not privy to(this is my first contribution), but I wanted to release this PR as a conduit for public discussion on the issue. Thoughts?

[obestwalter]

Updated the trivial conflict - let's see if we can bring this home, otherwise should be closed slowly as it was only intended to be a temporary fix.