support/scripts/pkg-stats: fix running on older python versions

Commit f71d9f49e546 (support/scripts/pkg-stats: fix datetime deprecation
warning) forgot to consider that the datetime.UTC suggested by python
3.12, was only introduced with python 3.11.

However, we are still generating the daily report on a python 3.8
version, which fails at runtime:
    AttributeError: module 'datetime' has no attribute 'UTC'

It turns out that datetime.UTC is just an alias for datetime.timezone.utc,
which seems to have existed since before python3...

Use datetime.timezone.utc instead of its alias.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/scripts/pkg-stats

@@ -1290,7 +1290,7 @@ def __main__():
         package_list = set([v["name"] for v in show_info_js.values() if 'name' in v])
     else:
         package_list = None
-    date = datetime.datetime.now(datetime.UTC)
+    date = datetime.datetime.now(datetime.timezone.utc)
     commit = subprocess.check_output(['git', '-C', brpath,
                                       'rev-parse',
                                       'HEAD']).splitlines()[0].decode()