Fix tests fragile to PATH
Closes #21450

Get path of current python interpreter running opposed to one on users path.

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21453?src=pr&el=h1) Report
> Merging [#21453](https://codecov.io/gh/pandas-dev/pandas/pull/21453?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ab668b0a56a9f2aee959bde787e9a0af4068d7a7?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21453/graphs/tree.svg?height=150&src=pr&token=eZ4WkYLtcO&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/21453?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21453      +/-   ##
==========================================
- Coverage   91.89%   91.89%   -0.01%     
==========================================
  Files         153      153              
  Lines       49600    49600              
==========================================
- Hits        45580    45578       -2     
- Misses       4020     4022       +2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.29% <ø> (-0.01%)` | :arrow_down: |
| #single | `41.86% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21453?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/21453/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.6% <0%> (-0.21%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21453?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/21453?src=pr&el=footer). Last update [ab668b0...e846c18](https://codecov.io/gh/pandas-dev/pandas/pull/21453?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @WillAyd 