BLD: Bump Cython version from 0.23 to 0.24
- [X] closes #18613 
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

For the whatsnew:

- Used the same whatsnew message as was used during the last cython version bump in 0.20
- Moved some previous entries that were under the main "Backwards incompatible API changes" section to the "Other API Changes" subsection.