test_bot/formulae: re-enable all tests on Tier 1

[cho-m]

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Restore running all tests on Linux. This attempts a fix of sticky bit issue by avoiding chmod +t within vendor-gems

Keep a minimal set of tests for Tier 3 macOS runners as they often fail from older versions of commands.

[Copilot]

Pull request overview

Updates the test_bot portable-ruby workflow to (1) avoid GitHub Actions–specific behavior during brew vendor-gems and (2) restore running the full Homebrew test suite on Tier 1 runners while keeping a reduced set on non–Tier 1 configurations.

Changes:

• Unset GITHUB_ACTIONS for brew vendor-gems invocations to avoid the GitHub Actions Linux sticky-bit chmod +t behavior.
• Run full brew tests --online --coverage on Tier 1; keep --only=cask,formula on non–Tier 1.
• Reuse a shared no_github_actions_env hash for multiple steps (including the nested brew test-bot call).

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[cho-m]

May need a different fix if we hit permission issue running vendor-gems.

Possible ideas if this fails: undo chmod +t step in test-bot (at minimum for container.gz), skip Gzip test if sticky bit is set on test file, make Gzip unpack always remove sticky bit.