Fix Event Modification test Data

This patch fixes the data used for testing the event modification API
which was no proper JSON before, causing all failure tests to fail with
the same error.

tests/test_restapi.py

@@ -236,11 +236,19 @@ def test_modify_event(self):
         args = dict(headers=self.headers)
 
         # With authentication but no or invalid data
-        for data in (None,
-                     '{"type":"event","id":0,"attributes":{"invalid":0}}',
-                     '{"type":"event","id":0,"attributes":\
-                     {"status":"invalid"}}'):
-            args['data'] = {'data': [data]}
+        for data in (
+                None,
+                {
+                    'type': 'event',
+                    'id': 0,
+                    'attributes': {'invalid': 0}
+                },
+                {
+                    'type': 'event',
+                    'id': 0,
+                    'attributes': {'status': 'invalid'}
+                }):
+            args['data'] = json.dumps({'data': [data]})
             with ui.app.test_request_context(**args):
                 response = ui.jsonapi.modify_event(0)
                 self.assertEqual(response.status_code, 400)