fix: Call json_safe on globals in codejail remote_exec (#36542)

We need to make globals JSON-friendly before sending them across the
network.

Addresses https://github.com/edx/edx-arch-experiments/issues/1016

xmodule/capa/safe_exec/tests/test_remote_exec.py

@@ -0,0 +1,32 @@
+"""
+Tests for remote codejail execution.
+"""
+
+import json
+from unittest import TestCase
+from unittest.mock import patch
+
+from django.test import override_settings
+
+from xmodule.capa.safe_exec.remote_exec import get_remote_exec
+
+
+class TestRemoteExec(TestCase):
+    """Tests for remote_exec."""
+
+    @override_settings(
+        ENABLE_CODEJAIL_REST_SERVICE=True,
+        CODE_JAIL_REST_SERVICE_HOST='http://localhost',
+    )
+    @patch('requests.post')
+    def test_json_encode(self, mock_post):
+        get_remote_exec({
+            'code': "out = 1 + 1",
+            'globals_dict': {'some_data': b'bytes', 'unusable': object()},
+            'extra_files': None,
+        })
+
+        mock_post.assert_called_once()
+        data_arg = mock_post.call_args_list[0][1]['data']
+        payload = json.loads(data_arg['payload'])
+        assert payload['globals_dict'] == {'some_data': 'bytes'}