[cmake] Try to apply git patch for metis only once.
Should fix errors when NOT using CPM_SOURCE_CACHE
such as
error: programs/CMakeLists.txt: patch does not apply
Follow-up on !4773 (merged).
Attention: If you delete the CMakeCache.txt then you have to delete build/_deps/metis-* as well!
Edited by Dmitry Yu. Naumov