Avoid instantiating deserialize_any for KeyClassifier

Deserialize_str involves compiling less code.

Author: dtolnay

src/value/de.rs

@@ -1301,7 +1301,7 @@ impl<'de> DeserializeSeed<'de> for KeyClassifier {
     where
         D: serde::Deserializer<'de>,
     {
-        deserializer.deserialize_any(self)
+        deserializer.deserialize_str(self)
     }
 }