Replace deprecated datetime.utcfromtimestamp

It was deprecated in Python 3.12 due to datetime.fromtimestamp[1].

[1] https://docs.python.org/3/library/datetime.html#datetime.datetime.utcfromtimestamp

Change-Id: I939080262e095e4f151f804c8364b8fa6a99162a

cloudkitty/utils/__init__.py

@@ -67,21 +67,24 @@ def iso8601_from_timestamp(timestamp, microsecond=False):
     """Returns an iso8601 formatted date from timestamp"""
 
     # Python provides a similar instance method for datetime.datetime
-    # objects called isoformat() and utcfromtimestamp(). The format
-    # of the strings generated by isoformat() and utcfromtimestamp()
+    # objects called isoformat() and fromtimestamp(). The format
+    # of the strings generated by isoformat() and fromtimestamp()
     # have a couple of problems:
     # 1) The method iso8601_from_timestamp in oslo_utils is realized
     #    by isotime, the strings generated by isotime are used in
     #    tokens and other public APIs that we can't change without a
     #    deprecation period. The strings generated by isoformat are
     #    not the same format, so we can't just change to it.
-    # 2) The strings generated by isoformat() and utcfromtimestamp()
+    # 2) The strings generated by isoformat() and fromtimestamp()
     #    do not include the microseconds if the value happens to be 0.
     #    This will likely show up as random failures as parsers may be
     #    written to always expect microseconds, and it will parse
     #    correctly most of the time.
 
-    return isotime(datetime.datetime.utcfromtimestamp(timestamp), microsecond)
+    return isotime(
+        datetime.datetime.fromtimestamp(timestamp, tz=datetime.timezone.utc),
+        microsecond
+    )
 
 
 def dt2ts(orig_dt):
@@ -100,7 +103,8 @@ def ts2dt(timestamp):
     """timestamp to datetime format."""
     if not isinstance(timestamp, float):
         timestamp = float(timestamp)
-    return datetime.datetime.utcfromtimestamp(timestamp)
+    return datetime.datetime.fromtimestamp(
+        timestamp, tz=datetime.timezone.utc).replace(tzinfo=None)
 
 
 def ts2iso(timestamp):