Fix clippy lint.

src/lib.rs

@@ -98,7 +98,7 @@ pub async fn local_trigger(payload: &str) -> Result<(), Box<dyn std::error::Erro
 
     let allowed_repos = std::env::var("WEBHOOK_BRIDGE_REPO_WHITELIST")
         .ok()
-        .unwrap_or_else(String::new);
+        .unwrap_or_default();
     let allowed_repos: HashSet<_> = allowed_repos
         .split(",")
         .filter(|s| !s.is_empty())