python 3.12: utcnow function is deprecated

The following warning is displayed on a system running with Python 3.12:
-------------------
/usr/lib/python3.12/site-packages/ipalib/rpc.py:925: DeprecationWarning:
datetime.utcnow() is deprecated and scheduled for removal in a future
version. Use timezone-aware objects to represent datetimes in UTC:
datetime.now(datetime.UTC).

  timestamp=datetime.datetime.utcnow())
-------------------

Fixes: https://pagure.io/freeipa/issue/9425
Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>

ipapython/certdb.py

@@ -943,7 +943,7 @@ class NSSDatabase:
     def _verify_cert_validity(self, cert):
         """Common checks for cert validity
         """
-        utcnow = datetime.datetime.utcnow()
+        utcnow = datetime.datetime.now(tz=datetime.UTC)
         if cert.not_valid_before > utcnow:
             raise ValueError(
                 f"not valid before {cert.not_valid_before} UTC is in the "

ipapython/cookie.py

@@ -652,7 +652,7 @@ class Cookie:
 
         cookie_expiration = self.get_expiration()
         if cookie_expiration is not None:
-            now = datetime.datetime.utcnow()
+            now = datetime.datetime.now(tz=datetime.UTC)
             if cookie_expiration < now:
                 raise Cookie.Expired("cookie named '%s'; expired at %s'" % \
                                      (cookie_name,