beefy: error logs for validators with dummy keys (#3939)

This outputs:
```
2024-04-02 14:36:02.135 ERROR tokio-runtime-worker beefy: 🥩 for session starting at block 21990151
no BEEFY authority key found in store, you must generate valid session keys
(https://wiki.polkadot.network/docs/maintain-guides-how-to-validate-polkadot#generating-the-session-keys)
```
error log entry, once every session, for nodes running with
`Role::Authority` that have no public BEEFY key in their keystore

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/client/consensus/beefy/src/tests.rs

@@ -379,6 +379,7 @@ async fn voter_init_setup(
 		Arc::new(api.clone()),
 		&key_store,
 		&metrics,
+		true,
 	)
 	.await
 }
@@ -438,6 +439,7 @@ where
 			min_block_delta,
 			prometheus_registry: None,
 			on_demand_justifications_handler: on_demand_justif_handler,
+			is_authority: true,
 		};
 		let task = crate::start_beefy_gadget::<_, _, _, _, _, _, _>(beefy_params);