Utilities/Doxygen/mcdoc.py chokes on non-existent include directory

```log
Start 1042: ITKIOMeshInDoxygenGroup

1042: Test command: "C:\Program Files\Python312\python.exe" "C:/Misc/ITK-patches2/CMake/../Utilities/Doxygen/mcdoc.py" "check" "ITKIOMesh" "C:/Misc/ITK-patches2/Modules/IO/Mesh/include"
1042: Working Directory: C:/Misc/ITK-patches2-vs22/Modules/IO/Mesh
1042: Test timeout computed to be: 1500
1042: Traceback (most recent call last):
1042: File "C:\Misc\ITK-patches2\Utilities\Doxygen\mcdoc.py", line 195, in
1042: ret = main()
1042: ^^^^^^
1042: File "C:\Misc\ITK-patches2\Utilities\Doxygen\mcdoc.py", line 161, in main
1042: ret = max(ret, checkGroup(fname, module))
1042: ^^^^^^^^^^^^^^^^^^^^^^^^^
1042: File "C:\Misc\ITK-patches2\Utilities\Doxygen\mcdoc.py", line 85, in checkGroup
1042: f = open(fname, encoding="utf-8")
1042: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1042: FileNotFoundError: [Errno 2] No such file or directory: 'C:/Misc/ITK-patches2/Modules/IO/Mesh/include'
1/1 Test #1042: ITKIOMeshInDoxygenGroup ..........***Failed 0.08 sec
```