Store boolean values in Redis as valid JSON

Calling `.set()` with `True` stores the byte string `'True'` which
cannot subsequently be decoded from JSON (because boolean values in
JSON are lowercase, ie `true`).

app/notify_client/job_api_client.py

@@ -90,7 +90,7 @@ class JobApiClient(NotifyAdminAPIClient):
 
         self.redis_client.set(
             'has_jobs-{}'.format(service_id),
-            True,
+            b'true',
             ex=cache.TTL,
         )
 

tests/app/notify_client/test_job_client.py

@@ -29,7 +29,7 @@ def test_client_creates_job_data_correctly(mocker, fake_uuid):
     mock_post.assert_called_once_with(url=expected_url, data=expected_data)
     mock_redis_set.assert_called_once_with(
         'has_jobs-{}'.format(service_id),
-        True,
+        b'true',
         ex=604800,
     )