Add None to SubsegmentContextManager.__enter__ return type (#13892)

Author: tmlnv

stubs/aws-xray-sdk/aws_xray_sdk/core/models/subsegment.pyi

@@ -20,7 +20,7 @@ class SubsegmentContextManager:
     subsegment: Subsegment
     def __init__(self, recorder: AWSXRayRecorder, name: Incomplete | None = None, **subsegment_kwargs) -> None: ...
     def __call__(self, wrapped, instance, args: list[Any], kwargs: dict[str, Any]): ...
-    def __enter__(self) -> Subsegment: ...
+    def __enter__(self) -> Subsegment | None: ...
     def __exit__(
         self, exc_type: type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None
     ) -> None: ...