After creating a new scene in a separate window when performing UI
tests, the respective view layer for the window may not be updated
immediately in the event loop.
Previously, this was mitigated with a single `yield` statement that
would delay processing by a single tick. To fix this issue, this commit
adds the capability to yield for a specific `timedelta` and waits this
amount of time for the two affected tests.
Pull Request: https://projects.blender.org/blender/blender/pulls/136012
