Fix doc to match function signature

[ticosax]

Update code example for batch_defer(). (Arguments need to be expanded)

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• [ ] Tests
  • [x] (not applicable?)
• [x] Documentation
  • [ ] (not applicable?)

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[ewjoachim]

I've switched to the simpler

await my_task.batch_defer_async(
    {"a": 1, "b": 2},
    {"a": 3, "b": 4},
    {"a": 5, "b": 6},
)

with a note on using my_task.batch_defer(*payloads).

[ewjoachim]

(Pyright is not working on main, we'll need to fix it before we can merge, sorry about that)

[ewjoachim]

Main is fixed, if you can rebase, PR should be green :) (I'd do it but while repo maintainers can add commits, we can't force-push, and I'd like to avoid merge commits)

[github-actions[bot]]

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