core-lightning: update livecheck

[samford]

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• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>?
• Is your test running fine brew test <formula>?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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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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The livecheck block for core-lightning checks the latest release on GitHub but upstream has introduced a two-week embargo period for 26.06.7, where they won't provide the source zip file as a release asset until the embargo is over (only binaries until then). I didn't find an alternative source to check for the latest source zip link, so this updates the livecheck block to use the GithubReleases strategy to check multiple releases to find the latest version with a source zip file. If this doesn't end up being a long-term strategy, we can return to the previous GithubLatest check in the future when the source zip is reliably provided at the time a release is published.