Failure to find classes in `ITKDoxygenTAG/InsightDoxygen.tag`

CI is failing with 6 warnings from missing TAG file definitions:

[CDash results](https://open.cdash.org/viewBuildError.php?type=1&buildid=7915737)

```none
2022-05-16T17:37:04.4831048Z /home/runner/work/bld/ITKEx-build/src/Filtering/ImageIntensity/AddConstantToEveryPixel/Documentation.rst:41: WARNING: doxygenclass: Cannot find class "itk::AddImageFilter" in doxygen xml output for project "ITK" from directory: /home/runner/work/bld/ITKEx-build/ITKDoxygenXML
2022-05-16T17:37:04.4832379Z /home/runner/work/bld/ITKEx-build/src/Filtering/ImageIntensity/AddConstantToEveryPixel/Documentation.rst:41: WARNING: Could not find match for `itk::AddImageFilter` in `/home/runner/work/bld/ITKEx-build/ITKDoxygenTAG/InsightDoxygen.tag` tag file. Error reported was Could not find a match
2022-05-16T17:37:04.4833848Z /home/runner/work/bld/ITKEx-build/src/Filtering/ImageIntensity/AddTwoImages/Documentation.rst:34: WARNING: doxygenclass: Cannot find class "itk::AddImageFilter" in doxygen xml output for project "ITK" from directory: /home/runner/work/bld/ITKEx-build/ITKDoxygenXML
2022-05-16T17:37:04.4875018Z /home/runner/work/bld/ITKEx-build/src/Filtering/ImageIntensity/AddTwoImages/Documentation.rst:34: WARNING: Could not find match for `itk::AddImageFilter` in `/home/runner/work/bld/ITKEx-build/ITKDoxygenTAG/InsightDoxygen.tag` tag file. Error reported was Could not find a match
2022-05-16T17:37:04.5222485Z /home/runner/work/bld/ITKEx-build/src/Numerics/Statistics/CreateHistogramFromListOfMeasurements/Documentation.rst:45: WARNING: doxygenclass: Cannot find class "itk::Statistics::SampleToHistogramFilter" in doxygen xml output for project "ITK" from directory: /home/runner/work/bld/ITKEx-build/ITKDoxygenXML
2022-05-16T17:37:04.5251169Z /home/runner/work/bld/ITKEx-build/src/Numerics/Statistics/CreateHistogramFromListOfMeasurements/Documentation.rst:45: WARNING: Could not find match for `itk::Statistics::SampleToHistogramFilter` in `/home/runner/work/bld/ITKEx-build/ITKDoxygenTAG/InsightDoxygen.tag` tag file. Error reported was Could not find a match
```

CI for [https://github.com/InsightSoftwareConsortium/ITKSphinxExamples/commit/e49dee5b6c515679376da8235c6dd79e99fc755d](https://github.com/InsightSoftwareConsortium/ITKSphinxExamples/commit/e49dee5b6c515679376da8235c6dd79e99fc755d) passed when first run on May 9th and then failed when re-run on May 16th.

[https://github.com/InsightSoftwareConsortium/ITKSphinxExamples/blob/master/CMake/DownloadDoxygenTAG.cmake](https://github.com/InsightSoftwareConsortium/ITKSphinxExamples/blob/master/CMake/DownloadDoxygenTAG.cmake) shows that the DoxygenTAG file is located at [https://itk.org/files/NightlyDoxygen/InsightDoxygenDocTag.gz](https://itk.org/files/NightlyDoxygen/InsightDoxygenDocTag.gz). Downloading, decompressing, and inspecting this file shows that it does include definitions for `AddImageFilter` and `SampleToHistogramFilter`.