gh-84649: Fix unstable test_rollover_at_midnight (GH-154463)

gh-84649: Fix unstable test_rollover_at_midnight (GH-154463)

Create the log file in a fresh directory under a name which has never
been used.  On Windows, NTFS file tunneling restored the original
creation time of a file recreated with the same name, which made the
rollover time earlier than the current time and caused an unwanted
rollover.

Also check that the rollover does not happen before the specified time.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>