tests: link board_wdt_early_stub in TriCore integ builds

- startup.S calls ulmk_board_wdt_disable_early; CMake already had the
  weak stub but whitebox Makefiles did not, breaking ctx_early_tricore CI

Author: uLipe

tests/arch/tricore.mk

@@ -17,6 +17,7 @@ ARCH_LDFLAGS := -mcpu=tc39xx
 
 ARCH_KERNEL_SRCS := \
 	$(ROOT)/arch/tricore/startup.S \
+	$(ROOT)/arch/tricore/board_wdt_early_stub.S \
 	$(ROOT)/arch/tricore/arch.c \
 	$(ROOT)/arch/tricore/smp.c \
 	$(ROOT)/arch/tricore/ctx_switch.S \