Fix test-related issues (#17888)

* Remove obsolete RSS::Serializer test

Since #17828, RSS::Serializer no longer has specific code for deleted statuses,
but it is never called on deleted statuses anyway.

* Rename erroneously-named test files

* Fix failing test

* Fix test deprecation warnings

* Update CircleCI Ruby orb

1.4.0 has a bug that does not match all the test files due to incorrect
globbing

spec/lib/html_aware_formatter_spec.rb

@@ -0,0 +1,44 @@
+require 'rails_helper'
+
+RSpec.describe HtmlAwareFormatter do
+  describe '#to_s' do
+    subject { described_class.new(text, local).to_s }
+
+    context 'when local' do
+      let(:local) { true }
+      let(:text) { 'Foo bar' }
+
+      it 'returns formatted text' do
+        is_expected.to eq '<p>Foo bar</p>'
+      end
+    end
+
+    context 'when remote' do
+      let(:local) { false }
+
+      context 'given plain text' do
+        let(:text) { 'Beep boop' }
+
+        it 'keeps the plain text' do
+          is_expected.to include 'Beep boop'
+        end
+      end
+
+      context 'given text containing script tags' do
+        let(:text) { '<script>alert("Hello")</script>' }
+
+        it 'strips the scripts' do
+          is_expected.to_not include '<script>alert("Hello")</script>'
+        end
+      end
+
+      context 'given text containing malicious classes' do
+        let(:text) { '<span class="mention  status__content__spoiler-link">Show more</span>' }
+
+        it 'strips the malicious classes' do
+          is_expected.to_not include 'status__content__spoiler-link'
+        end
+      end
+    end
+  end
+end