Don't extract plaintext from script and style tags

The content of a `script` or `style` tag shouldn't be included
in the plaintext conversion of a node.

actiontext/lib/action_text/plain_text_conversion.rb

@@ -22,11 +22,17 @@ def plain_text_for_node(node, index = 0)
       def plain_text_for_node_children(node)
         texts = []
         node.children.each_with_index do |child, index|
+          next if skippable?(child)
+
           texts << plain_text_for_node(child, index)
         end
         texts.join
       end
 
+      def skippable?(node)
+        node.name == "script" || node.name == "style"
+      end
+
       def plain_text_method_for_node(node)
         :"plain_text_for_#{node.name}_node"
       end

actiontext/test/unit/plain_text_conversion_test.rb

@@ -144,6 +144,30 @@ class ActionText::PlainTextConversionTest < ActiveSupport::TestCase
     )
   end
 
+  test "script tags are ignored" do
+    assert_converted_to(
+      "Hello world!",
+      <<~HTML
+        <script type="javascript">
+          console.log("message");
+        </script>
+        <div><strong>Hello </strong>world!</div>
+      HTML
+    )
+  end
+
+  test "style tags are ignored" do
+    assert_converted_to(
+      "Hello world!",
+      <<~HTML
+        <style type="text/css">
+          body { color: red; }
+        </style>
+        <div><strong>Hello </strong>world!</div>
+      HTML
+    )
+  end
+
   private
     def assert_converted_to(plain_text, html)
       assert_equal plain_text, ActionText::Content.new(html).to_plain_text