Alerting: Fix flakey silence test (#61395)

public/app/features/alerting/unified/Silences.test.tsx

@@ -268,7 +268,6 @@ describe('Silence edit', () => {
 
       const start = new Date();
       const end = new Date(start.getTime() + 24 * 60 * 60 * 1000);
-      const now = dateTime().format('YYYY-MM-DD HH:mm');
 
       const startDateString = dateTime(start).format('YYYY-MM-DD');
       const endDateString = dateTime(end).format('YYYY-MM-DD');
@@ -312,7 +311,7 @@ describe('Silence edit', () => {
         expect(mocks.api.createOrUpdateSilence).toHaveBeenCalledWith(
           'grafana',
           expect.objectContaining({
-            comment: `created ${now}`,
+            comment: expect.stringMatching(/created (\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2})/),
             matchers: [
               { isEqual: true, isRegex: false, name: 'foo', value: 'bar' },
               { isEqual: false, isRegex: false, name: 'bar', value: 'buzz' },