Fix error in Notebook security context docs

This is wrong:

"Run as pipeline activity: The execution is triggered from Fabric Data Factory pipeline. You can find the detail steps in the Notebook Activity. The execution would be running under the pipeline owner's security context."

https://learn.microsoft.com/en-us/fabric/data-engineering/how-to-use-notebook#security-context-of-running-notebook

The reality is that "The execution would be running under the pipeline's Last Modified By user's security context."

Please update the docs to reflect the reality 🙂