ENH: Added index to testing assert message when series values differ
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This implements the suggestion made in #31190 
In short, where the values in 2 series differ, the assert exception message includes the index as well as the values.  This helps when using assert_frame_equal with check_like=True, since the index may be reordered, making the output hard to understand.