`itkStatisticsUniqueLabelMapFilterTest1` sometimes fails in CI

### Description

`itkStatisticsUniqueLabelMapFilterTest1` recently started failing in CI. Observed failures on both Windows and macOS.

### Steps to Reproduce

Run `itkStatisticsUniqueLabelMapFilterTest1` and compare output to baseline

### Expected behavior

Test passes

### Actual behavior

Output image differs from baseline

```none
2022-05-25T18:35:15.2139324Z 1883: Trying writer->Update()
2022-05-25T18:35:15.2140727Z 1883: 15
2022-05-25T18:35:15.2142370Z 1883: 15
2022-05-25T18:35:15.2143798Z 1883: 82
2022-05-25T18:35:15.2145256Z 1883: 82
2022-05-25T18:35:15.2146854Z 1883: 82
2022-05-25T18:35:15.2175541Z 1883: D:/a/1/s-build/Testing/Temporary/itkStatisticsUniqueLabelMapFilterTest1.png.diff.png
2022-05-25T18:35:15.2177873Z 1883: D:/a/1/s-build/Testing/Temporary/itkStatisticsUniqueLabelMapFilterTest1.png.base.png
2022-05-25T18:35:15.2180062Z 1883: D:/a/1/s-build/Testing/Temporary/itkStatisticsUniqueLabelMapFilterTest1.png.test.png
2022-05-25T18:35:15.2182290Z 1883: cthead1Label-label-statistics-unique-labelmap-baseline1.png
2022-05-25T18:35:15.2278622Z 1884: Trying writer->Update()
2022-05-25T18:35:15.2290186Z 1884: libpng warning: sCAL: invalid unit
2022-05-25T18:35:15.2301284Z 1884: libpng warning: sCAL: invalid unit
2022-05-25T18:35:15.2306662Z 1883: 0
2022-05-25T18:35:15.2339238Z 1883: cthead1Label-label-statistics-unique-labelmap-dilate-baseline1.png
2022-05-25T18:35:15.2653717Z 1884/2779 Test #1883: itkStatisticsUniqueLabelMapFilterTest1 .................................................................***Failed 0.24 sec
```

### Reproducibility

### Versions

`master`

### Environment

[macOS failure in CDash](https://open.cdash.org/test/706315444)

[Windows failure in CDash](https://open.cdash.org/test/707104926)

### Additional Information