Fix for changed error message in python 3.12rc

Author: adamchainz

tox.ini

@@ -16,6 +16,6 @@ commands =
       -W error::DeprecationWarning \
       -W error::PendingDeprecationWarning \
       -W ignore:'pkg_resources is deprecated as an API':DeprecationWarning \
-      -W ignore:'datetime.utcfromtimestamp() is deprecated':DeprecationWarning \
+      -W ignore:'daettime.datetime.utcfromtimestamp() is deprecated':DeprecationWarning \
       -m coverage run \
       -m pytest -p no:randomly {posargs:tests}