IonQ: Explicitly select lang (quantumlib#5348)

We were planning on making this arg optional, but it shouldn't hurt to also send it explicitly

Author: Cynocracy

cirq-ionq/cirq_ionq/ionq_client.py

@@ -118,7 +118,11 @@ def create_job(
         """
         actual_target = self._target(target)
 
-        json: Dict[str, Any] = {'target': actual_target, 'body': serialized_program.body}
+        json: Dict[str, Any] = {
+            'target': actual_target,
+            'lang': 'json',
+            'body': serialized_program.body,
+        }
         if name:
             json['name'] = name
         # We have to pass measurement keys through the metadata.

cirq-ionq/cirq_ionq/ionq_client_test.py

@@ -102,6 +102,7 @@ def test_ionq_client_create_job(mock_post):
 
     expected_json = {
         'target': 'qpu',
+        'lang': 'json',
         'body': {'job': 'mine'},
         'name': 'bacon',
         'shots': '200',