Don't load when the underlying class isn't available, such as when using WP CLI.

wp-redis-user-session-storage.php

@@ -22,6 +22,13 @@ along with this program; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
+/**
+ * Don't load in contexts that lack the WP_Session_Tokens class
+ */
+if ( ! class_exists( 'WP_Session_Tokens' ) ) {
+	return;
+}
+
 /**
  * Redis-based user sessions token manager.
  *