Update UnitTestError.cxx

The stack frame depth on Andes is lower than the unit test:

117: Test command: /ccs/home/nthompson/vtk-m/build/bin/UnitTests_vtkm_cont_testing "UnitTestError" "-v" "INFO" "--data-dir=/ccs/home/nthompson/vtk-m/data/data" "--baseline-dir=/ccs/home/nthompson/vtk-m/data/baseline" "--write-dir=/ccs/home/nthompson/vtk-m/build"
117: Test timeout computed to be: 180
117: date       time         ( uptime  ) [ thread name/id ]                   file:line     v|
117: 2021-04-16 13:44:54.222 (   0.000s) [main thread     ]             loguru.cpp:591   Info| arguments: UnitTestError -v INFO --data-dir=/ccs/home/nthompson/vtk-m/data/data --baseline-dir=/ccs/home/nthompson/vtk-m/data/baseline --write-dir=/ccs/home/nthompson/vtk-m/build
117: 2021-04-16 13:44:54.222 (   0.000s) [main thread     ]             loguru.cpp:594   Info| Current dir: /autofs/nccs-svm1_home1/nthompson/vtk-m/build/vtkm/cont/testing
117: 2021-04-16 13:44:54.222 (   0.000s) [main thread     ]             loguru.cpp:596   Info| stderr verbosity: 0
117: 2021-04-16 13:44:54.222 (   0.000s) [main thread     ]             loguru.cpp:597   Info| -----------------------------------
117: 2021-04-16 13:44:54.222 (   0.000s) [main thread     ]      UnitTestError.cxx:67    Info| Check base error messages
117: Error at /ccs/home/nthompson/vtk-m/vtkm/cont/testing/UnitTestError.cxx:57:ValidateError
117: 	Expected more entries in the stack frame
117: 3             0x51aade /ccs/home/nthompson/vtk-m/build/bin/UnitTests_vtkm_cont_testing() [0x51aade]
117: 2       0x7f0d785db873 __libc_start_main + 243
117: 1             0x516581 /ccs/home/nthompson/vtk-m/build/bin/UnitTests_vtkm_cont_testing() [0x516581]
117: 0             0x486e51 /ccs/home/nthompson/vtk-m/build/bin/UnitTests_vtkm_cont_testing() [0x486e51] (count > 4)
117: 2021-04-16 13:44:54.222 (   0.000s) [main thread     ]             loguru.cpp:471   Info| atexit
3/3 Test #117: UnitTestError .......................***Failed    0.00 sec