[Merge] ~nteodosio/update-manager:a11y-read-checkbox-state into update-manager:main

[Nathan Teodosio]

I tested this in 25.04 and 24.10 with sufficiently complex (with multiple levels of nesting) package lists. As I'm convinced that this is working alright, I'm submitting it to review.
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https://code.launchpad.net/~nteodosio/update-manager/+git/update-manager/+merge/479006
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~nteodosio/update-manager:a11y-read-checkbox-state into update-manager:main.