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
Hello @TomAugspurger! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/extension/test_sparse.py`](https://github.com/TomAugspurger/pandas/blob/f534f0ec591e1bec3e2febaa8bd2e7ff7541b3bf/pandas/tests/extension/test_sparse.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23323?src=pr&el=h1) Report
> Merging [#23323](https://codecov.io/gh/pandas-dev/pandas/pull/23323?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/1c26375c0743a2cbdcfe14a62ad10806001cbee8?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23323/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23323?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23323   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files         169      169           
  Lines       50911    50911           
=======================================
  Hits        46954    46954           
  Misses       3957     3957
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.65% <ø> (ø)` | :arrow_up: |
| #single | `42.29% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23323?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23323?src=pr&el=footer). Last update [1c26375...f534f0e](https://codecov.io/gh/pandas-dev/pandas/pull/23323?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
