Googletest export

add missing using ::testing::DoAll when DoAll used in example

PiperOrigin-RevId: 402416497

docs/gmock_cook_book.md

@@ -1980,6 +1980,7 @@ If the mock method also needs to return a value as well, you can chain
 
 ```cpp
 using ::testing::_;
+using ::testing::DoAll;
 using ::testing::Return;
 using ::testing::SetArgPointee;