COMP: Update Doxygen XML and HTML artifacts to v6.0b01

The v5.3.0 Doxygen run generated no class compounds for
itk::AddImageFilter and itk::Statistics::SampleToHistogramFilter,
breaking their breathelink lookups; v6.0b01 contains both and matches
the ITK main the examples build. The DocTag asset is still 5.3.0 (v6
releases publish none), so its lookup exception remains.

Author: hjmjohnson

CMake/CTestCustom.cmake.in

@@ -46,6 +46,9 @@ set(CTEST_CUSTOM_WARNING_EXCEPTION
   "LabelGeometryImageFilter.*deprecated"
   "note: declared here"
   "RemovedInSphinx[0-9]+Warning"
+  # The newest published InsightDoxygenDocTag is 5.3.0, which lacks some
+  # class compounds; drop once ITK releases publish a current tag asset.
+  "Could not find match for .itk::"
   "ipo: warning #11053"
   "ipo: warning #11053"
   "vxl.core.vnl.algo"

CMake/DownloadDoxygen.cmake

@@ -1,3 +1,3 @@
-file(DOWNLOAD https://github.com/InsightSoftwareConsortium/ITK/releases/download/v5.3.0/InsightDoxygenDocHtml-5.3.0.tar.gz
+file(DOWNLOAD https://github.com/InsightSoftwareConsortium/ITK/releases/download/v6.0b01/InsightDoxygenDocHtml-6.0b01.tar.gz
   ${ITKDoxygen_TEMP_DIR}/itk-doxygen.tar.gz SHOW_PROGRESS
   )

CMake/DownloadDoxygenTAG.cmake

@@ -1,3 +1,4 @@
+# v6 releases do not yet publish an InsightDoxygenDocTag asset; 5.3.0 is the newest.
 file(DOWNLOAD https://github.com/InsightSoftwareConsortium/ITK/releases/download/v5.3.0/InsightDoxygenDocTag-5.3.0.gz
   ${ITKDoxygenTAG_TEMP_DIR}/InsightDoxygen.tag.gz SHOW_PROGRESS
   )

CMake/DownloadDoxygenXML.cmake

@@ -1,3 +1,3 @@
-file(DOWNLOAD https://github.com/InsightSoftwareConsortium/ITK/releases/download/v5.3.0/InsightDoxygenDocXml-5.3.0.tar.gz
+file(DOWNLOAD https://github.com/InsightSoftwareConsortium/ITK/releases/download/v6.0b01/InsightDoxygenDocXml-6.0b01.tar.gz
   ${ITKDoxygenXML_TEMP_DIR}/itk-doxygen-xml.tar.gz SHOW_PROGRESS
   )