feat(tvix/nar-bridge): change default port

Having `tvix-store daemon` and `nar-bridge` listen on the same port by
default is silly.
Use the same port that nar-bridge-go was using previously.

Change-Id: Id374a12e52ba9dac4318e43d0ca0853866eadabc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11998
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: yuka <yuka@yuka.dev>
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>

tvix/nar-bridge/src/bin/nar-bridge.rs

@@ -74,7 +74,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
         .with_state(state);
 
     let listen_address = &cli.listen_args.listen_address.unwrap_or_else(|| {
-        "[::]:8000"
+        "[::]:9000"
             .parse()
             .expect("invalid fallback listen address")
     });