Set HOMEBREW_DEBUG when running brew tests --debug

- This will cause the "debug" gem to be required in `spec_helper.rb`, so we can do interactive debugging.

Library/Homebrew/dev-cmd/tests.rb

@@ -45,8 +45,6 @@ def run
         # Given we might be testing various commands, we probably want everything (except sorbet-static)
         Homebrew.install_bundler_gems!(groups: Homebrew.valid_gem_groups - ["sorbet"])
 
-        require "debug" if args.debug?
-
         HOMEBREW_LIBRARY_PATH.cd do
           setup_environment!
 
@@ -137,6 +135,8 @@ def run
 
           puts "Randomized with seed #{seed}"
 
+          ENV["HOMEBREW_DEBUG"] = "1" if args.debug? # Used in spec_helper.rb to require the "debug" gem.
+
           # Submit test flakiness information using BuildPulse
           # BUILDPULSE used in spec_helper.rb
           if use_buildpulse?

Library/Homebrew/test/migrator_spec.rb

@@ -69,8 +69,6 @@
       tab.source["tap"] = "homebrew/core"
       tab.write
 
-      binding.b
-
       expect do
         described_class.new(new_formula, "oldname")
       end.to raise_error(Migrator::MigratorDifferentTapsError)

Library/Homebrew/test/spec_helper.rb

@@ -37,6 +37,8 @@
 
 require_relative "../global"
 
+require "debug" if ENV["HOMEBREW_DEBUG"]
+
 require "test/support/quiet_progress_formatter"
 require "test/support/helper/cask"
 require "test/support/helper/files"