Use ghcr.io/homebrew/brew:main for tests and bottling

[cho-m]

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Will need to check on any regressions in Homebrew/core afterward.

In theory, ghcr.io/homebrew/ubuntu22.04:main should be identical to ghcr.io/homebrew/brew:main for now.

[Copilot]

Pull request overview

Updates Homebrew’s GitHub Actions Linux container image references to use the consolidated ghcr.io/homebrew/brew:main image, aligning runner specs and generated CI matrices with the new canonical tag used for Homebrew’s Docker-based CI/testing.

Changes:

• Switch Linux runner container image in GitHubRunnerMatrix from ghcr.io/homebrew/ubuntu22.04:main to ghcr.io/homebrew/brew:main.
• Update generate-cask-ci-matrix Linux container image output to ghcr.io/homebrew/brew:main.
• Update the Linux x86_64 test-bot job container in .github/workflows/tests.yml to ghcr.io/homebrew/brew:main.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
Library/Homebrew/github_runner_matrix.rb	Uses ghcr.io/homebrew/brew:main for Linux runner container specs produced for tap CI matrices.
Library/Homebrew/dev-cmd/generate-cask-ci-matrix.rb	Emits ghcr.io/homebrew/brew:main for Linux cask CI jobs.
.github/workflows/tests.yml	Runs Linux x86_64 test-bot inside ghcr.io/homebrew/brew:main instead of the Ubuntu 22.04 tag.

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[MikeMcQuaid]

Looks good when comment addressed!