[rubygems/rubygems] Add a spec to cover what vendoring timeout fixes

rubygems/rubygems@2662e45d75

spec/bundler/runtime/inline_spec.rb

@@ -615,4 +615,29 @@ def confirm(msg, newline = nil)
 
     expect(err).to eq("The Gemfile specifies no dependencies")
   end
+
+  it "does not load default timeout" do
+    default_timeout_version = ruby "gem 'timeout', '< 999999'; require 'timeout'; puts Timeout::VERSION", raise_on_error: false
+    skip "timeout isn't a default gem" if default_timeout_version.empty?
+
+    # This only works on RubyGems 3.5.0 or higher
+    ruby "require 'rubygems/timeout'", raise_on_error: false
+    skip "rubygems under test does not yet vendor timeout" unless last_command.success?
+
+    build_repo4 do
+      build_gem "timeout", "999"
+    end
+
+    script <<-RUBY
+      require "bundler/inline"
+
+      gemfile(true) do
+        source "#{file_uri_for(gem_repo4)}"
+
+        gem "timeout"
+      end
+    RUBY
+
+    expect(out).to include("Installing timeout 999")
+  end
 end