BUG: df.pivot_table: margins_name is ignored when there aggfunc is li…
- [x ] closes #13354 
- [ ] tests added / passed
- [ ] passes `git diff upstream/master | flake8 --diff`
- [ ] whatsnew entry

…st #13354

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13363?src=pr) is **84.23%**

> Merging [#13363](https://codecov.io/gh/pydata/pandas/pull/13363?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #13363   diff @@
==========================================
  Files           138        138          
  Lines         50724      50724          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          42726      42725     -1   
- Misses         7998       7999     +1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [103f7d3...f7cd79f](https://codecov.io/gh/pydata/pandas/compare/103f7d31e1b850e532ed85a4b53ef222d1271c54...f7cd79f6d5c1cd6346199737b4feafc1ff7c8d2f)
 can you add tests / rebase
 can you rebase / update?
 closing, but pls reopen / comment if you can continue

needs tests
