Update teams.ipynb

[kmstar307]

When executed the result is "None" on aborting teams.

Why are these changes needed?

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[ekzhu]

@kmstar307 I am not sure what do you mean? The code prints "Task was cancelled".

[kmstar307]

When the agent teams is aborted with cancellation token, as per documentation it should throw exception but the the result is coming as "None"

[kmstar307]

@ekzhu

[ekzhu]

The code is not returning anything as it prints the message. I don't this fix is necessary.