workflows/tests: simulate macOS for brew style homebrew-core

[Rylan12]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

We currently run brew style homebrew/core twice in the tap syntax (Linux) workflow, but both times the Homebrew/linuxbrew-core repo is checked. THis PR adds HOMEBREW_SIMULATE_MACOS_ON_LINUX=1 to the second brew style call so that Homebrew/homebrew-core is checked.

[BrewTestBot]

Review period skipped due to critical label.

[MikeMcQuaid]

THis PR adds HOMEBREW_SIMULATE_MACOS_ON_LINUX=1 to the second brew style call so that Homebrew/homebrew-core is checked.

This will happen without it because it's already tapped. If linuxbrew-core is tapped it won't try to retap homebrew-core (and vice-versa). No harm in adding, though 👍🏻

[Rylan12]

Ah, yes, I see now 👍

No preference, then, for whether to merge or not