fix(docs/cpp): fix error: comparison of integer expressions of different signedness: ‘size_t’ {aka ‘long unsigned int’} and ‘int’ [-Werror=sign-compare]

codes/cpp/chapter_array_and_linkedlist/list.cpp

@@ -48,8 +48,8 @@ int main() {
     PrintUtil::printVector(list);
 
     /* 通过索引遍历列表 */
-    int count = 0;
-    for (int i = 0; i < list.size(); i++) {
+    size_t count = 0;
+    for (size_t i = 0; i < list.size(); i++) {
         count++;
     }