Update fixed mx version.

Mx checkout-downstream needs @mx.no_suite_loading.

Author: ansalond

common.jsonnet

@@ -36,7 +36,7 @@ local common_json = (import "common.json");
 
   local common = python3 + {
     packages+: {
-      'mx': '5.279.2',
+      'mx': '5.280.3',
       'pip:pylint': '==1.9.3',
       'pip:ninja_syntax': '==1.7.2',
     },