fix MacPython / pandas-wheels ci failures
xref https://github.com/pandas-dev/pandas/pull/25452#issuecomment-468654194

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=h1) Report
> Merging [#25505](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/011f0a6ebacb13619bf8225b3bc2370872b85769?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/25505/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25505   +/-   ##
=======================================
  Coverage   91.75%   91.75%           
=======================================
  Files         173      173           
  Lines       52955    52955           
=======================================
  Hits        48589    48589           
  Misses       4366     4366
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.32% <ø> (ø)` | :arrow_up: |
| #single | `41.72% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25505?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/25505?src=pr&el=footer). Last update [011f0a6...c6d0972](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=h1) Report
> Merging [#25505](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/011f0a6ebacb13619bf8225b3bc2370872b85769?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/25505/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25505   +/-   ##
=======================================
  Coverage   91.75%   91.75%           
=======================================
  Files         173      173           
  Lines       52955    52955           
=======================================
  Hits        48589    48589           
  Misses       4366     4366
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.32% <ø> (ø)` | :arrow_up: |
| #single | `41.72% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25505?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/25505?src=pr&el=footer). Last update [011f0a6...c6d0972](https://codecov.io/gh/pandas-dev/pandas/pull/25505?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
