Fix pytest collection warning (#3651)

Fixes a pytest collection warning because the test class starts with the
prefix "Test"

tests/unit_tests/output_parsers/test_pydantic_parser.py

@@ -23,6 +23,10 @@ class TestModel(BaseModel):
     )
 
 
+# Prevent pytest from trying to run tests on TestModel
+TestModel.__test__ = False  # type: ignore[attr-defined]
+
+
 DEF_RESULT = """{
     "action": "Update",
     "action_input": "The PydanticOutputParser class is powerful",