Fix clippy issues

Author: esteve

rclrs/src/node/subscription.rs

@@ -218,13 +218,13 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{create_node, Context, Subscription, QOS_PROFILE_DEFAULT};
+    use crate::{create_node, Context, QOS_PROFILE_DEFAULT};
 
     #[test]
     fn test_instantiate_subscriber() -> Result<(), RclrsError> {
         let context =
             Context::new(vec![]).expect("Context instantiation is expected to be a success");
-        let node = create_node(&context, "test_new_subscriber")?;
+        let mut node = create_node(&context, "test_new_subscriber")?;
         let _subscriber = node.create_subscription::<std_msgs::msg::String, _>(
             "test",
             QOS_PROFILE_DEFAULT,