Fix a few RedundantCast

Reported by psalm
For #25641

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

apps/federation/lib/DbHandler.php

@@ -87,7 +87,7 @@ class DbHandler {
 		$result = $query->execute();
 
 		if ($result) {
-			return (int)$this->connection->lastInsertId('*PREFIX*'.$this->dbTable);
+			return $query->getLastInsertId();
 		}
 
 		$message = 'Internal failure, Could not add trusted server: ' . $url;

apps/files_external/lib/Service/DBConfigService.php

@@ -267,7 +267,7 @@ class DBConfigService {
 				'type' => $builder->createNamedParameter($type, IQueryBuilder::PARAM_INT)
 			]);
 		$query->execute();
-		return (int)$this->connection->lastInsertId('*PREFIX*external_mounts');
+		return $query->getLastInsertId();
 	}
 
 	/**