Update to code to Rust 1.67

src/tcp_relay_client/mod.rs

@@ -76,7 +76,7 @@ pub async fn run_app(mut args: ClientConfig) -> std::io::Result<()> {
         Err(e) => {
             Err(std::io::Error::new(
                 ErrorKind::Other,
-                format!("Failed to fetch relay configuration from server! {}", e),
+                format!("Failed to fetch relay configuration from server! {e}"),
             ))?;
             unreachable!();
         }