Add Ruby 3.0 support (#16046)

* Fix issues with POSIX::Spawn, Terrapin and Ruby 3.0

Also improve the Terrapin monkey-patch for the stderr/stdout issue.

* Fix keyword argument handling throughout the codebase

* Monkey-patch Paperclip to fix keyword arguments handling in validators

* Change validation_extensions to please CodeClimate

* Bump microformats from 4.2.1 to 4.3.1

* Allow Ruby 3.0

* Add Ruby 3.0 test target to CircleCI

* Add test for admin dashboard warnings

* Fix admin dashboard warnings on Ruby 3.0

spec/models/session_activation_spec.rb

@@ -74,13 +74,13 @@ RSpec.describe SessionActivation, type: :model do
     let(:options) { { user: Fabricate(:user), session_id: '1' } }
 
     it 'calls create! and purge_old' do
-      expect(described_class).to receive(:create!).with(options)
+      expect(described_class).to receive(:create!).with(**options)
       expect(described_class).to receive(:purge_old)
-      described_class.activate(options)
+      described_class.activate(**options)
     end
 
     it 'returns an instance of SessionActivation' do
-      expect(described_class.activate(options)).to be_kind_of SessionActivation
+      expect(described_class.activate(**options)).to be_kind_of SessionActivation
     end
   end