source-genesys: fix conversations default param bug

In Python, default parameters are evaluated once when the function
definition is executed. This means that a default param of
`datetime.now(tz=UTC)` is only evaluated when the program starts up,
and that same value is used for each subsequent function call. Meaning
that within the connector, `_perform_conversation_job` was using a fixed
end date and not incrementing it over time.

Now, a default value of `None` is used in `_perform_conversation_job`
to indicate that the current time should be used as the end date.

source-genesys/source_genesys/api.py

@@ -87,13 +87,17 @@ async def _perform_conversation_job(
         domain: str,
         log: Logger,
         start_date: datetime,
-        end_date: datetime = datetime.now(tz=UTC),
+        end_date: datetime | None = None,
 ) -> AsyncGenerator[Conversation, None]:
     """
     Requests the Genesys API to perform an async job & paginates through the results.
 
     API docs - https://developer.genesys.cloud/routing/conversations/conversations-apis#post-api-v2-analytics-conversations-details-jobs
     """
+
+    if end_date is None:
+        end_date = datetime.now(tz=UTC)
+
     # Submit job.
     url = f"{COMMON_API}.{domain}/api/v2/analytics/conversations/details/jobs"
     body = {