fix(gossipsub): allow clippy beta lint (#3321)

It doesn't appear that rust-lang/rust-clippy#10061 is going to be fixed any time soon. In the meantime, our CI is "red" which is misleading because we purposely don't require this CI check. It will however hit stable in ~ 2 weeks at which point our required clippy CI check will fail.

Suppress clippy lint with an `allow` to make it pass.

protocols/gossipsub/src/behaviour.rs

@@ -1416,6 +1416,8 @@ where
                                 peer_score.add_penalty(peer_id, 1);
 
                                 // check the flood cutoff
+                                // See: https://github.com/rust-lang/rust-clippy/issues/10061
+                                #[allow(unknown_lints, clippy::unchecked_duration_subtraction)]
                                 let flood_cutoff = (backoff_time
                                     + self.config.graft_flood_threshold())
                                     - self.config.prune_backoff();