TST: Parametrize tests in tests/util/test_hashing.py
Noticed that these tests could be parametrized when investigating a comment in the `IntervalArray` PR, and originally started doing to work there.  The `IntervalArray` PR is big enough already, and this is unrelated, so creating a separate PR.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21883?src=pr&el=h1) Report
> Merging [#21883](https://codecov.io/gh/pandas-dev/pandas/pull/21883?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/bdb61688aa80a6ec9bdb6832946dd83ab4b4c9c8?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/21883/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21883?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21883   +/-   ##
=======================================
  Coverage   91.91%   91.91%           
=======================================
  Files         164      164           
  Lines       49992    49992           
=======================================
  Hits        45952    45952           
  Misses       4040     4040
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <ø> (ø)` | :arrow_up: |
| #single | `42.16% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21883?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/21883?src=pr&el=footer). Last update [bdb6168...3124d0c](https://codecov.io/gh/pandas-dev/pandas/pull/21883?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @jschendel 