added experimental flag for tests

Author: mertcanaltin

test/parallel/test-log-basic.js

@@ -1,4 +1,5 @@
 'use strict';
+// Flags: --experimental-logger
 
 const common = require('../common');
 

test/parallel/test-logger-serializers.js

@@ -1,4 +1,5 @@
 'use strict';
+// Flags: --experimental-logger
 
 require('../common');
 const assert = require('assert');