BUG: AssertionError on Series.append(DataFrame) fix  #30975 
- [x] closes #30975 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Series.append() does not throw AssertionError anymore. This fix performs a precheck before proceeding with concatenation. Tests have passed. Whatsnew entry added.
Thanks!
Hello @hvardhan20! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-01-21 06:02:52 UTC This seems fine for backport.

What's the plan for 1.0.1 / 1.1? For this to raise a TypeError? Do we have an issue for that? thanks @hvardhan20 

can you open an issue as @TomAugspurger suggest https://github.com/pandas-dev/pandas/pull/31036#issuecomment-577248825