CI: Fix Assign CI not working with quotes
- [x] closes #29768 
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Examples(all three passed)
![image](https://user-images.githubusercontent.com/47963215/72952081-a6481100-3d45-11ea-8845-338f2a2f17a4.png)


Thanks for working on this. Do you know why this works? I'm wondering if it's because the content of the variable is assigned and taking a substring is having no effect.  @datapythonista I think I got it now. 
Can you take another look? Thanks.  Thanks @lithomas1, I think this fix is better than what I proposed.

For the next time, I recommend you use a hit branch, and not work directly in master.

(Just trying " this, to see if it works as expected). 