adapt signature of DatabaseSessionHandler::gc to the parent class

src/Session/DatabaseSessionHandler.php

@@ -86,12 +86,12 @@ class DatabaseSessionHandler implements ISessionHandler
         return true;
     }
 
-    public function gc($maxlifetime): bool
+    public function gc($maxlifetime): int|false
     {
         // empty on purpose
         // old sessions are deleted by MaintainDatabaseCommand
 
-        return true;
+        return 1;
     }
 
     public function create_sid(): string