[rubygems/rubygems] Added example for legacy windows platform

https://github.com/rubygems/rubygems/commit/90130c0648

spec/bundler/other/major_deprecation_spec.rb

@@ -573,6 +573,38 @@ RSpec.describe "major deprecations" do
     end
   end
 
+  context "bundle install with a lockfile including X64_MINGW_LEGACY platform" do
+    before do
+      gemfile <<~G
+        source "https://gem.repo1"
+        gem "rake"
+      G
+
+      lockfile <<~L
+        GEM
+          remote: https://rubygems.org/
+          specs:
+            rake (10.3.2)
+
+        PLATFORMS
+          ruby
+          x64-mingw32
+
+        DEPENDENCIES
+          rake
+
+        BUNDLED WITH
+           #{Bundler::VERSION}
+      L
+    end
+
+    it "raises a helpful error" do
+      bundle "install", raise_on_error: false
+
+      expect(err).to include("Found x64-mingw32 in lockfile, which is no longer supported as of Bundler 4.0.")
+    end
+  end
+
   context "when Bundler.setup is run in a ruby script" do
     before do
       create_file "gems.rb", "source 'https://gem.repo1'"