Fix backward compatible Pundit include (thoughtbot#2383)

This commit fixes thoughtbot#2378
by adding a conditional that includes Pundit::Authorization when it is
defined else it includes Pundit.

This change ensures that we remain compatible with Pundit < 2.2.0

To test with Pundit "~> 2.1.0", we run:

```
bundle exec appraisal pundit21 rspec spec/controllers/concerns/administrate/punditize_spec.rb
```

See: thoughtbot#2141
See: thoughtbot#1068

Appraisals

@@ -9,3 +9,7 @@ end
 appraise "rails70" do
   gem "rails", "~> 6.1"
 end
+
+appraise "pundit21" do
+  gem "pundit", "~> 2.1.0"
+end

app/controllers/concerns/administrate/punditize.rb

@@ -2,7 +2,12 @@ module Administrate
   module Punditize
     if Object.const_defined?("Pundit")
       extend ActiveSupport::Concern
-      include Pundit::Authorization
+
+      if Pundit.const_defined?(:Authorization)
+        include Pundit::Authorization
+      else
+        include Pundit
+      end
 
       included do
         private

gemfiles/pundit21.gemfile

@@ -0,0 +1,49 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+ruby "3.2.2"
+
+gem "administrate-field-image"
+gem "faker"
+gem "front_matter_parser"
+gem "globalid"
+gem "kaminari-i18n"
+gem "pg"
+gem "pundit", "~> 2.1.0"
+gem "redcarpet"
+gem "sentry-raven"
+gem "unicorn"
+
+group :development, :test do
+  gem "appraisal"
+  gem "awesome_print"
+  gem "byebug"
+  gem "dotenv-rails"
+  gem "factory_bot_rails"
+  gem "i18n-tasks", "1.0.12"
+  gem "pry"
+  gem "yard"
+end
+
+group :test do
+  gem "ammeter"
+  gem "capybara"
+  gem "database_cleaner"
+  gem "formulaic"
+  gem "launchy"
+  gem "selenium-webdriver"
+  gem "shoulda-matchers"
+  gem "timecop"
+  gem "webdrivers"
+  gem "webmock"
+  gem "webrick"
+  gem "xpath", "3.2.0"
+end
+
+group :staging, :production do
+  gem "rack-timeout"
+  gem "uglifier"
+end
+
+gemspec path: "../"

spec/controllers/concerns/administrate/punditize_spec.rb

@@ -8,9 +8,26 @@ module Administrate
       end
     end
 
+    unless Pundit.const_defined?(:Authorization)
+      # Spec for pundit < 2.2
+      it "exists when Pundit::Authorization is not defined" do
+        reload_punditize
+        expect(Pundit.const_defined?(:Authorization)).to be_falsey
+        expect { build_dummy }.not_to raise_error
+      end
+    end
+
     def unload_constants
       original = Pundit
       Object.send(:remove_const, "Pundit")
+      reload_punditize
+
+      yield
+
+      Object.const_set("Pundit", original)
+    end
+
+    def reload_punditize
       Administrate.send(:remove_const, "Punditize")
       load Rails.root.join(
         "..",
@@ -21,10 +38,6 @@ def unload_constants
         "administrate",
         "punditize.rb",
       )
-
-      yield
-
-      Object.const_set("Pundit", original)
     end
 
     def dummy_class