[utest] 添加 signal 依赖项

examples/utest/testcases/kernel/Kconfig

@@ -39,6 +39,7 @@ config UTEST_MESSAGEQUEUE_TC
 
 config UTEST_SIGNAL_TC
     bool "signal test"
+    select RT_USING_SIGNALS
     default n
 
 config UTEST_MUTEX_TC