fix imageurl in notification test

skip unnecessary http -> https redirect, which could make problems on some notifiers

pkg/services/alerting/test_notification.go

@@ -56,7 +56,7 @@ func createTestEvalContext(cmd *NotificationTestCommand) *EvalContext {
 
 	ctx := NewEvalContext(context.Background(), testRule)
 	if cmd.Settings.Get("uploadImage").MustBool(true) {
-		ctx.ImagePublicUrl = "http://grafana.org/assets/img/blog/mixed_styles.png"
+		ctx.ImagePublicUrl = "https://grafana.com/assets/img/blog/mixed_styles.png"
 	}
 	ctx.IsTestRun = true
 	ctx.Firing = true