Fix cargo clippy issues

src/client.rs

@@ -38,7 +38,7 @@ impl OpenIDConfig {
         code: &str,
         redirect_uri: &str,
     ) -> Result<(OpenIDTokenResponse, String), Box<dyn Error>> {
-        let authorization = BASE64_STANDARD.encode(format!("{}:{}", client_id, client_secret));
+        let authorization = BASE64_STANDARD.encode(format!("{client_id}:{client_secret}"));
 
         let mut params = HashMap::new();
         params.insert("grant_type", "authorization_code");