transmission-cli: add livecheck strategy

[samford]

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

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Currently, livecheck uses the PageMatch strategy for the GitHub repository URL used in the transmission-cli livecheck block, since the Git strategy doesn't apply to it. We check the main GitHub page for this project because this repository simply contains archive files.

The Git strategy will apply to this URL if/when Homebrew/brew#9074 is merged, so I'm preemptively specifying the strategy here to prevent this check from breaking. This check is already using the PageMatch strategy, so this doesn't alter the current behavior and there's no harm in defensively adding it here.