docs: update Vale styles

[p-linnane]

For Homebrew/brew.sh#1338.

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[Copilot]

Pull request overview

Updates Homebrew’s Vale “Headings” style exceptions so certain proper nouns/acronyms are allowed in non-h1 headings without being flagged as not sentence case.

Changes:

• Add ARM64 to the heading sentence-case exceptions list.
• Add Golden Gate to the heading sentence-case exceptions list.

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