superproject: Log syncstate's parameter as data-json it it is an array.

All the values of syncstate are strings, check the first byte and last
byte to see if it is an array. For syncstate data, there were no false
positives.

Tested:
$ repo_dev sync

Verified event logged for argv is "data-json".

$./run_tests

Bug: [google internal] b/201102002
Change-Id: Id56adb532b80267f08d09147ac663cdd5987ce87
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/319075
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Raman Tenneti <rtenneti@google.com>

tests/test_git_trace2_event_log.py

@@ -267,7 +267,7 @@ class EventLogTestCase(unittest.TestCase):
       self.assertIn('value', event)
       key = event['key'].removeprefix(f'{prefix_value}/')
       value = event['value']
-      self.assertEqual(self._event_log_module.GetDataEventName(key), event['event'])
+      self.assertEqual(self._event_log_module.GetDataEventName(value), event['event'])
       self.assertTrue(key in config and value == config[key])
 
   def test_error_event(self):