test: update test_util.cc for coverage

update test_util.cc for code coverage src/util-inl.h:PopFront()

PR-URL: #55291
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: kmk324

test/cctest/test_util.cc

@@ -27,6 +27,7 @@ TEST_F(UtilTest, ListHead) {
 
   List list;
   EXPECT_TRUE(list.IsEmpty());
+  EXPECT_TRUE(list.PopFront() == nullptr);
 
   Item one;
   EXPECT_TRUE(one.node_.IsEmpty());