FIX: Do not allow invite_only and enable_sso at the same time

This functionality was never supported but before the new review queue
it didn't have any errors. Now the combination of settings is prevented
and existing sites with sso enabled will be migrated to remove invite
only.

spec/components/validators/enable_invite_only_validator_spec.rb

@@ -0,0 +1,31 @@
+require 'rails_helper'
+
+RSpec.describe EnableInviteOnlyValidator do
+  subject { described_class.new }
+
+  context "when sso is enabled" do
+    before do
+      SiteSetting.sso_url = "https://example.com/sso"
+      SiteSetting.enable_sso = true
+    end
+
+    it "is valid when false" do
+      expect(subject.valid_value?('f')).to eq(true)
+    end
+
+    it "is isn't value for true" do
+      expect(subject.valid_value?('t')).to eq(false)
+      expect(subject.error_message).to eq(I18n.t(
+        'site_settings.errors.sso_invite_only'
+      ))
+    end
+  end
+
+  context "when sso isn't enabled" do
+    it "is valid when true or false" do
+      expect(subject.valid_value?('f')).to eq(true)
+      expect(subject.valid_value?('t')).to eq(true)
+    end
+  end
+
+end

spec/components/validators/enable_sso_validator_spec.rb

@@ -26,6 +26,24 @@ RSpec.describe EnableSsoValidator do
       end
     end
 
+    describe "when invite_only is set" do
+      before do
+        SiteSetting.invite_only = true
+        SiteSetting.sso_url = 'https://example.com/sso'
+      end
+
+      it 'allows a false value' do
+        expect(subject.valid_value?('f')).to eq(true)
+      end
+
+      it "doesn't allow true" do
+        expect(subject.valid_value?('t')).to eq(false)
+        expect(subject.error_message).to eq(I18n.t(
+          'site_settings.errors.sso_invite_only'
+        ))
+      end
+    end
+
     describe "when 'sso url' is present" do
       before do
         SiteSetting.sso_url = "https://www.example.com/sso"