[cmake][python][bugfix] Add WORKING_DIRECTORY argument back

The argument has been accidentally removed in !1130.
This causes the WORKING_DIRECTORY argument being parsed
as one of the MULTI argmuents if following one of these
and can break the dune_add_test call.

cmake/modules/DunePythonTestCommand.cmake

@@ -40,7 +40,7 @@ include_guard(GLOBAL)
 function(dune_python_add_test)
   # Parse Arguments
   set(OPTION)
-  set(SINGLE NAME)
+  set(SINGLE NAME WORKING_DIRECTORY)
   set(MULTI SCRIPT MODULE CMAKE_GUARD LABELS TIMEOUT)
   cmake_parse_arguments(PYTEST "" "${SINGLE}" "${MULTI}" ${ARGN})
   if(PYTEST_COMMAND)
@@ -54,6 +54,10 @@ function(dune_python_add_test)
     set(PYTEST_TIMEOUT 3600)
   endif()
 
+  if(NOT PYTEST_WORKING_DIRECTORY)
+    set(PYTEST_WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+  endif()
+
   if((NOT PYTEST_MODULE) AND (NOT PYTEST_SCRIPT))
     message(FATAL_ERROR "dune_python_add_test: Either SCRIPT or MODULE need to be specified!")
   endif()
@@ -83,6 +87,7 @@ function(dune_python_add_test)
                 PYTHON_TEST
                 CMAKE_GUARD ${PYTEST_CMAKE_GUARD}
                 LABELS ${PYTEST_LABELS}
+                WORKING_DIRECTORY ${PYTEST_WORKING_DIRECTORY}
                 TIMEOUT ${PYTEST_TIMEOUT}
                 ${PYTEST_UNPARSED_ARGUMENTS}
                )