Stop serializing timezone-naive datetime to timezone-aware dateime wi…

…th UTC tz (#36379)

airflow/serialization/serializers/datetime.py

@@ -24,7 +24,6 @@
     serialize as serialize_timezone,
 )
 from airflow.utils.module_loading import qualname
-from airflow.utils.timezone import convert_to_utc, is_naive
 
 if TYPE_CHECKING:
     import datetime
@@ -45,10 +44,8 @@ def serialize(o: object) -> tuple[U, str, int, bool]:
 
     if isinstance(o, datetime):
         qn = qualname(o)
-        if is_naive(o):
-            o = convert_to_utc(o)
 
-        tz = serialize_timezone(o.tzinfo)
+        tz = serialize_timezone(o.tzinfo) if o.tzinfo else None
 
         return {TIMESTAMP: o.timestamp(), TIMEZONE: tz}, qn, __version__, True
 
@@ -83,7 +80,11 @@ def deserialize(classname: str, version: int, data: dict | str) -> datetime.date
             else:
                 tz = timezone(data[TIMEZONE])
         else:
-            tz = deserialize_timezone(data[TIMEZONE][1], data[TIMEZONE][2], data[TIMEZONE][0])
+            tz = (
+                deserialize_timezone(data[TIMEZONE][1], data[TIMEZONE][2], data[TIMEZONE][0])
+                if data[TIMEZONE]
+                else None
+            )
 
     if classname == qualname(datetime.datetime) and isinstance(data, dict):
         return datetime.datetime.fromtimestamp(float(data[TIMESTAMP]), tz=tz)

tests/serialization/serializers/test_serializers.py

@@ -84,6 +84,11 @@ def test_datetime(self):
         d = deserialize(s)
         assert i.timestamp() == d.timestamp()
 
+        i = datetime.datetime.now()
+        s = serialize(i)
+        d = deserialize(s)
+        assert i.timestamp() == d.timestamp()
+
     def test_deserialize_datetime_v1(self):
         s = {
             "__classname__": "pendulum.datetime.DateTime",