fix: add operation_context to DummyConfig in test_enum_optionset_payload

The hand-rolled DummyConfig stub was missing the new operation_context
attribute, causing _ODataClient.__init__ to fail with AttributeError.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: arorashivam96

tests/unit/data/test_enum_optionset_payload.py

@@ -25,6 +25,7 @@ def __init__(self, language_code=1033):
         self.http_backoff = 0
         self.http_timeout = 5
         self.log_config = None
+        self.operation_context = None
 
 
 def _make_client(lang=1033):