prepare 8.2.1 release (#229)

## [8.2.1] - 2023-10-20
### Fixed:
- Replace deprecated `utcfromtimestamp` usage.

---------

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ldclient/impl/model/value_parsing.py

@@ -1,16 +1,16 @@
 import re
 from re import Pattern
 from semver import VersionInfo
-from datetime import tzinfo, timedelta, datetime
+from datetime import tzinfo, timedelta, datetime, timezone
 from numbers import Number
 from typing import Any, Optional
 
 import pyrfc3339
 
 _ZERO = timedelta(0)
 
-# A UTC class.
 
+# A UTC class.
 class _UTC(tzinfo):
  """UTC"""
 
@@ -23,7 +23,8 @@ def tzname(self, dt):
  def dst(self, dt):
  return _ZERO
 
-_epoch = datetime.utcfromtimestamp(0).replace(tzinfo=_UTC())
+
+_epoch = datetime.fromtimestamp(0, timezone.utc)
 
 
 def is_number(input: Any) -> bool: