TST: test that operations with Series(ExtensionArray) and list-likes work
xref https://github.com/pandas-dev/pandas/pull/22026/files#r212253565

Operations with Series holding an ExtensionArray and with a list as other operand work, eg:

```
In [29]: pd.Series([1, 2, 3], dtype='Int64') + [1, 2, 3]
Out[29]: 
0    2
1    4
2    6
dtype: Int64
```

but we should add an explicit test for it (now only test with other Series, and not for array / list)