github_runner_matrix: enable arm64 linux dep tests when not self-hosted

[cho-m]

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Increase arm64 Linux testing to now run on dependents as long as CI-linux-self-hosted-deps is not used.

As far as I can tell, arm64 Linux is faster than Intel Linux so should be able to finish within same time frame.

This should make our arm64 Linux support closer to complete "Tier 1" status. The remainder of CI either needs self-hosted runner or adding support for splitting dependent tests across separate jobs.

[Copilot]

Pull Request Overview

This PR enhances arm64 Linux testing by enabling it for dependent tests when not using self-hosted runners. Previously, arm64 Linux runners were excluded from all dependent matrix tests, but now they are only excluded when using the self-hosted runner (CI-linux-self-hosted-deps).

• Modifies the runner generation logic to conditionally include arm64 Linux runners based on whether self-hosted runners are being used
• Adds test coverage for both scenarios: dependent tests with and without self-hosted runners

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Library/Homebrew/github_runner_matrix.rb	Updates logic to only exclude arm64 Linux runner when using self-hosted runners for dependent tests
Library/Homebrew/test/github_runner_matrix_spec.rb	Adds test cases verifying arm64 Linux runner is included for non-self-hosted dependent tests and excluded for self-hosted ones

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[MikeMcQuaid]

Thanks!

[MikeMcQuaid]

The remainder of CI either needs self-hosted runner or adding support for splitting dependent tests across separate jobs.

Work continues on self-hosted work.

Splitting dependent tests would be very cool if we could do it, though. Means we could likely use GitHub runners a lot more on both macOS and Linux.