DOC/CI: add missing import to ipython directive in `whatsnew/v0.11.0.rst`
some of the builds have failed recently due to this ipython directive, so I added the fix as advised in the error warning.
no objection, but where did you see this? here: https://github.com/pandas-dev/pandas/pull/40926/checks?check_run_id=2341068381
and: https://github.com/pandas-dev/pandas/pull/40731/checks?check_run_id=2336499675
and: https://github.com/pandas-dev/pandas/pull/40422/checks?check_run_id=2340597878

3 different pull requests, all of which I don't think have anything to do with this error. Thanks!