DOC: Fix typo in docstring of DataFrame.memory_usage 
Cherry picked commit from #25761 and removed trailing whitespace.

@jorisvandenbossche if you don't mind taking a look
Looks good! (I merged since the failures are unrelated and master is already red, and it is already being handled elsewhere)

I added a "Co-authored-by: " note in the commit message when squashing on github, so the original author gets proper credit (otherwise, due to the squashing, it is only the user that opened the PR that becomes the commit author). Great thanks @jorisvandenbossche 