Fix typo

src/util.rs

@@ -57,7 +57,7 @@ where
 {
     let opt = Option::<String>::deserialize(de)?;
     // TODO: Switch to and remove this attribute `opt.as_deref()` once MSRV is >= 1.40
-    #[allow(clippy::clippy::option_as_ref_deref)]
+    #[allow(clippy::option_as_ref_deref)]
     let opt = opt.as_ref().map(String::as_str);
     match opt {
         None | Some("") => Ok(None),