DOC: Added section on git bisect to pandas maintenance
- [ ] closes #35685
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added an entry in the latest `doc/source/whatsnew/v1.6.0.rst` file if fixing a bug or adding a new feature.

Added section on regressions to development guide under pandas maintenance. Wasn't sure if this needs a whatsnew entry, added it anyway.

@MarcoGorelli Please let me know what you think.
@MarcoGorelli Thank you for the speedy feedback! The whatsnew entries are removed. Thanks @seljaks 