dune-testtools_SCRIPTS_DIR not defined

Running dunecontrol for dune-xt-la (which depends on dune-testtools) always results in a "//main77.cc not found" error because dune-testtools_SCRIPTS_DIR is not defined. Replacing line 182 in DuneSystemtests.cmake by

-          set(SOURCE_FILES ${dune-testtools_SCRIPTS_DIR}/main77.cc)
+          set(SOURCE_FILES ${dune-testtools_PREFIX}/cmake/scripts/main77.cc)

works for me.