TST: Update sparse data generation
There's a spurious failure on master when the first
is randomly chosen to be 0, since type(arr.fill_value) doesn't
match arr.dtype.type

https://github.com/pandas-dev/pandas/issues/23124 will fix the underlying issue, but this works around it so we don't have tests failing randomly.

Closes https://github.com/pandas-dev/pandas/issues/23168