Avoid install warning annotations

[MikeMcQuaid]

Fixes #22433

• Keep idempotent brew install warnings visible in CI logs.
• Avoid noisy GitHub Actions annotations for harmless installs.
• Preserve annotation behaviour for other opoo callers.

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[Copilot]

Pull request overview

This PR keeps harmless idempotent brew install warnings visible in GitHub Actions logs without emitting workflow annotations, while preserving existing annotation behavior for other warning callers.

Changes:

• Adds a warning helper that bypasses GitHub Actions annotations while still printing to stderr.
• Uses the helper for “already installed and up-to-date” install paths.
• Adds a utility output spec for the new helper.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
Library/Homebrew/utils/output.rb	Adds opoo_without_github_actions_annotation.
Library/Homebrew/install.rb	Routes selected idempotent install warnings through the new helper.
Library/Homebrew/test/utils/output_spec.rb	Adds coverage for the new output helper.

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