[ios] Fix test testLeaveSwitcherAfterEnteringAndExittingInactiveTabs

This CL adds a workaround to fix test in
TabSwitcherTransitionTestCase when run on iOS18 devices.

Bug: 349816094
Change-Id: I97c98787fc53c2abab43a0dfd27334ff6cf2dbe4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5713310
Auto-Submit: Federica Germinario <fedegermi@google.com>
Commit-Queue: Federica Germinario <fedegermi@google.com>
Reviewed-by: Louis Romero <lpromero@google.com>
Commit-Queue: Louis Romero <lpromero@google.com>
Cr-Commit-Position: refs/heads/main@{#1328141}