grandpa: update to finality-grandpa v0.12.0 (#5853)

* grandpa: update to v0.12.0

* grandpa: fix tests

* grandpa: better validation of authority set invariants

* grandpa: avoid duplicating invalid authority list check

* grandpa: add missing doc

* grandpa: better validation of expect proofs

* grandpa: fix test compilation

* grandpa: fix tests

* grandpa: add test for AuthoritySet invariants

* grandpa: bump finality-grandpa to v0.12.0

substrate/client/finality-grandpa/src/observer.rs

@@ -409,11 +409,13 @@ mod tests {
 			(Arc::new(client), backend)
 		};
 
+		let voters = vec![(sp_keyring::Ed25519Keyring::Alice.public().into(), 1)];
+
 		let persistent_data = aux_schema::load_persistent(
 			&*backend,
 			client.info().genesis_hash,
 			0,
-			|| Ok(vec![]),
+			|| Ok(voters),
 		).unwrap();
 
 		let (_tx, voter_command_rx) = tracing_unbounded("");