`creation_date` check made with local time

[aulemahal]

Minor issue I guess, but the checker told me that my "The 'creation_date' attribute is in the future" for a file I had just created.

The issue is that the attribute is defined as an UTC time, but the check uses:

cc-plugin-cc6/cc_plugin_cc6/base.py

Line 1875 in 50543d0

> dt.now()

I think it should use:

import datetime as dt

dt.datetime.now(dt.UTC)

I know I am in "euro-cordex", but still ;). I can submit a PR!