Fix more clippy warnings

src/database/models.rs

@@ -1915,7 +1915,7 @@ impl<'a> Object<'a> for Participant {
 
 fn make_name_valid(mut name: String) -> String {
     if let Err(error) = webhook_username(&name) {
-        if let ValidationErrorType::WebhookUsername { len, substring } = error.kind() {
+        if let ValidationErrorType::WebhookUsername { len, .. } = error.kind() {
             if let Some(len) = len {
                 if *len < 2 {
                     name = format!("{name}--");