test: disable warnings to fix flaky test

Fixes: #40738

PR-URL: #40739
Backport-PR-URL: #41776
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/message/esm_display_syntax_error_import_json_named_export.mjs

@@ -1,4 +1,4 @@
-// Flags: --experimental-json-modules
+// Flags: --experimental-json-modules --no-warnings
 /* eslint-disable no-unused-vars */
 import '../common/index.mjs';
 import { ofLife } from '../fixtures/experimental.json' assert { type: 'json' };