TST : Adding new test case for pivot_table() with Categorical data
TST: add additional test cases for pivot_table with categorical data #21370

- [x] closes #21370
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Added a new test case for checking ```index/column/value``` workability as per the patch offered by PR #21252 

**Note** : the _civ means Column,Index and Value in the test name (wasn't being very creative here)