The datetime.utcnow() is deprecated in Python 3.12.
Replace datetime.utcnow() with oslo_utils.timeutils.utcnow().
This bumps oslo.utils to 7.0.0.
Change-Id: Ic4e33df4fc9e858a9de139066feaaaec71bfc6fe
Signed-off-by: Takashi Natsume <takanattie@gmail.com>