test_bot/formulae: only run brew style if deps are bottled

[cho-m]

brew style needs to install Homebrew/core formulae to run, but portable Ruby PRs run on Tier 3 machines resulting in attempting to source build multiple formulae and failing.

For now, skip brew style when bottles are not available (i.e. for macOS machines). We can consider splitting workflow to 2 separate runners if we want to test this, i.e. bottling on Tier 3 while running further tests on Tier 1.

See https://github.com/Homebrew/homebrew-core/actions/runs/29198762997/job/86666911890?pr=292807#step:3:264

  ==> Installing shellcheck dependency: ghc
  ==> ./configure --prefix=/private/tmp/ghc-20260712-30776-z6focn/ghc-9.14.1/binar
  ==> make install
  ==> cabal v2-update
  ==> ./configure --disable-numa --with-system-libffi --with-gmp-includes=/opt/hom
  ==> hadrian/build install -j4 --prefix=/opt/homebrew/Cellar/ghc/9.14.1 --flavour
  Last 150 lines from /Users/brew/actions-runner/_work/homebrew-core/homebrew-core/bottles/logs/ghc/05.build.log:

---

• Have you followed our Contributing guidelines?
• Have you checked for other open Pull Requests for the same change?
• Have you explained what your changes do? Performance claims (e.g. "this is faster") must include Hyperfine benchmarks.
• Have you explained why you'd like these changes included, not just what they do?
• For bug fixes, have you given step-by-step brew commands to reproduce the bug?
• Have you written new tests (excluding integration tests)? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) locally?

---

• AI was used to generate or assist with generating this PR.

---

[Copilot]

Pull request overview

This PR adjusts Homebrew’s test-bot behavior for portable Ruby runs to avoid failing on Tier 3 macOS runners where brew style would otherwise trigger source builds of Homebrew/core formulae (due to missing bottles).

Changes:

• Gate brew style during portable-ruby validation on whether the actionlint, shellcheck, and shfmt formulae are bottled for the current platform.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[MikeMcQuaid]

Makes sense 👍🏻