Handle `CancelledError` in all uses of `Task.exception()`

[shsms]

What's needed?

Task.exception() returns caught exceptions as values, unless the caught exception is a CancelledError, in which case, it raises the CancelledError as well.

Our uses of Task.exception() might not be accounting for this behaviour and might need special handling if cancelling the parent task is not the right thing to do for any particular case.

Proposed solution

No response

Use cases

No response

Alternatives and workarounds

No response

Additional context

No response

[llucax]

I started working on this while we were talking about it.