Fixed slow-running scheduling default test

refs https://github.com/TryGhost/Team/issues/860

- Slow unit tests cause longer waiting time to deliver code to main. Before this fix the test was taking a whooping 6s on average
- The main cause of the delay was a downstream's package (got) default retry logic that was taking up a lot of time bypassing the retry logic present in the default scheduler itself

core/server/adapters/scheduling/SchedulingDefault.js

@@ -276,6 +276,7 @@ SchedulingDefault.prototype._pingUrl = function (object) {
     const options = {
         timeout: requestTimeout,
         method: httpMethod.toLowerCase(),
+        retry: 0,
         headers: {
             'Content-Type': 'application/json'
         }