CLN: Remove trailing commas
Working on: CLN remove unnecessary trailing commas to get ready for new version of black #35925.
Updated the following files: 
pandas/tests/series/methods/test_interpolate.py
pandas/tests/series/methods/test_unstack.py
pandas/tests/series/test_cumulative.py
pandas/tests/test_algos.py


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