address ambiguous auto variable. (ros2#2481) (ros2#2486)

Signed-off-by: Tomoya Fujita <[email protected]>
Signed-off-by: Steve Nogar <[email protected]>
(cherry picked from commit 3cdb259)

Co-authored-by: Tomoya Fujita <[email protected]>

Author: mergify[bot]

rclcpp/include/rclcpp/client.hpp

@@ -845,7 +845,7 @@ class Client : public ClientBase
         "Received invalid sequence number. Ignoring...");
       return std::nullopt;
     }
-    auto value = std::move(it->second.second);
+    std::optional<CallbackInfoVariant> value = std::move(it->second.second);
     this->pending_requests_.erase(request_number);
     return value;
   }