STYLE: mark the variable as advanced

Alex

Modules/FindPythonInterp.cmake

@@ -23,3 +23,6 @@ FIND_PROGRAM(PYTHON_EXECUTABLE
 # all listed variables are TRUE
 INCLUDE(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(PythonInterp DEFAULT_MSG PYTHON_EXECUTABLE)
+
+MARK_AS_ADVANCED(PYTHON_EXECUTABLE)
+