[rubygems/rubygems] Support PATH's using `File::ALT_SEPARATOR` in `Gem::Installer`

Co-authored-by: MSP-Greg <MSP-Greg@users.noreply.github.com>

https://github.com/rubygems/rubygems/commit/710b969b60

lib/rubygems/installer.rb

@@ -707,6 +707,8 @@ class Gem::Installer
     user_bin_dir = user_bin_dir.tr(File::ALT_SEPARATOR, File::SEPARATOR) if File::ALT_SEPARATOR
 
     path = ENV['PATH']
+    path = path.tr(File::ALT_SEPARATOR, File::SEPARATOR) if File::ALT_SEPARATOR
+
     if Gem.win_platform?
       path = path.downcase
       user_bin_dir = user_bin_dir.downcase

test/rubygems/test_gem_installer.rb

@@ -207,6 +207,16 @@ gem 'other', version
     end
 
     assert_empty @ui.error
+
+    return unless win_platform?
+
+    ENV['PATH'] = [orig_PATH, bin_dir.tr(File::SEPARATOR, File::ALT_SEPARATOR)].join(File::PATH_SEPARATOR)
+
+    use_ui @ui do
+      installer.check_that_user_bin_dir_is_in_path
+    end
+
+    assert_empty @ui.error
   ensure
     ENV['PATH'] = orig_PATH
   end