bricks/ev3rt/app: Fix code start area not set.

There isn't any code for this build but we should still set it to ensure a code size of 0.

bricks/ev3rt/app.c

@@ -27,6 +27,7 @@ void main_task(intptr_t unused) {
     while (true) {
         pbsys_main_program_t program = {
             .id = PBIO_PYBRICKS_USER_PROGRAM_ID_REPL,
+            .code_start = heap,
             .code_end = heap,
             .user_ram_start = heap,
             .user_ram_end = heap + sizeof(heap),