[iOS] Fix midnight issue for Safari reminder promo test

Test always fails when it is executed around midnight pacific time.
Updating it so the start time is "overridden" to be the midnight next
day.

Fixed: 442365426
Change-Id: Ide9364863d757487f0f353e64e310bd6c0829d81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6985741
Auto-Submit: Ginny Huang <ginnyhuang@chromium.org>
Reviewed-by: Robbie Gibson <rkgibson@google.com>
Commit-Queue: Robbie Gibson <rkgibson@google.com>
Cr-Commit-Position: refs/heads/main@{#1520850}