fix: keep reactions up to date even when read outside of effect

[dummdidumm]

In #17105 one line in update_reaction was changed that can cause reactivity loss. It checks if the reaction is updated inside of an effect and only then will push to the reactions. The prior version had an additional check to still add to the reactions if there is already at least one reaction on the derived, indicating it is connected. Removing this check fixes #17263 while keeping correctness: a connected derived by definition at least has one reaction and therefore can properly cleanup.

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