libpointing: add livecheck block

[botantony]

https://github.com/Homebrew/homebrew-core/actions/runs/31028968711/job/92384526495#step:6:16594

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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