workflows: enable Golden Gate bottling

[p-linnane]

This removes the macOS 27 upload guard so mass bottling can start, and refreshes the default branch in each workflow that runs brew pr-upload so its bottle coverage checks compare against current main.

tests now passes each runner the formula list its own matrix entry already carries, matching what test_deps does, so a Golden Gate runner builds only the formulae selected for it.

Requires Homebrew/brew#23918, which adds the coverage checks these workflows rely on. Merging that first is enough, since setup-homebrew resets the brew repo to origin/HEAD for tap repositories.

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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.

Claude Code (Opus 5) drafted the workflow changes; I reviewed the diff and ran actionlint.

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[MikeMcQuaid]

Nice!