Configuring with invalid value associated with VTK_BUILD_TESTING option incorrectly reports ENABLE_TESTS

Error message below should reported that argument for option VTK_BUILD_TESTING are incorrect and not option ENABLE_TESTS

Observed with a1625689

cmake -DVTK_BUILD_TESTING:STRING=YES .
CMake Error at CMake/vtkModule.cmake:563 (message):
  The `ENABLE_TESTS` argument must be one of `ON`, `OFF`, `WANT`, or
  `DEFAULT`.  Received `YES`.
Call Stack (most recent call first):
  CMakeLists.txt:270 (vtk_module_scan)