Fix useSubscription restart was not cached

[DoctorJohn]

This PR fixes that the useSubscription hook's definition of the recently added (#11927) restart function was not cached between rerenders (unlike refetch and fetchMore returned by similar hooks). This made the restart function unsuitable to be included in the dependency array of React.useEffect.

My use case is restarting a subscription when a React Native app is resumed from the background. @phryneas I assume it's evident from the code that restart is redefined every render. However, if you would like a reproducible, please let me know.

[apollo-cla]

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Latest commit: 5842753

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[phryneas]

Great catch, thank you for the contribution!
I'll clean that up a bit and get it released in a few minutes :)