Use short reference for monitors of dead processes

Author: mat-hek

src/libAtomVM/nifs.c

@@ -4456,7 +4456,7 @@ static term nif_erlang_monitor(Context *ctx, int argc, term argv[])
             RAISE_ERROR(OUT_OF_MEMORY_ATOM);
         }
         uint64_t ref_ticks = globalcontext_get_ref_ticks(ctx->global);
-        term ref = term_make_process_reference(ctx->process_id, ref_ticks, &ctx->heap);
+        term ref = term_from_ref_ticks(ref_ticks, &ctx->heap);
         term down_message_tuple = term_alloc_tuple(5, &ctx->heap);
         term_put_tuple_element(down_message_tuple, 0, DOWN_ATOM);
         term_put_tuple_element(down_message_tuple, 1, ref);