frame_methods benchmarking sum instead of mean
Not sure if the function name or the method call is incorrect, but it looks like this should be benchmarking `mean` instead of `sum`


## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/14824?src=pr) is 85.26% (diff: 100%)


> No coverage report found for **master** at e991141.

> Powered by [Codecov](https://codecov.io?src=pr). Last update [e991141...654057d](https://codecov.io/gh/pandas-dev/pandas/compare/e991141f3c13117035fb2a08f4e64b4c18c9d5a9...654057dfd03e63978c50c7608e4bf401ddb96110?src=pr) @mroeschke Looks ok, you will only have to rebase as I just merged a large PR cleaning-up lots of benchmarks (but your change can still be applied) Rebased and all green @jorisvandenbossche  thanks!