test: deprecate return false in test

[cho-m]

• 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 lgtm (style, typechecking and tests) with your changes locally?

---

Replacement for #21291 to allow odeprecate cycle.

Using BasicObject as we have no control over what a formula test block returns and we need something that supports ==.

[Copilot]

Pull request overview

This PR deprecates the use of return false to indicate test failure in Homebrew formula tests, encouraging the use of explicit exceptions instead. This is part of a gradual migration (allowing for an odeprecate cycle) to phase out this legacy behavior.

• Adds deprecation warning when a test returns false, guiding users to use raise instead
• Updates type signatures from T.nilable(T::Boolean) or T.untyped to BasicObject to support the transition period
• Includes TODO comments marking where code can be simplified once the deprecation cycle is complete

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
Library/Homebrew/test.rb	Adds detection and deprecation warning for return false in tests, along with TODOs for future cleanup
Library/Homebrew/formula.rb	Updates type signatures for run_test, test methods to use BasicObject instead of boolean types, with TODOs for reverting to void after deprecation cycle
Library/Homebrew/debrew.rb	Updates type signature for the test method override to match the new BasicObject return type

---

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

[MikeMcQuaid]

Thanks!