Change video with to 400 in element_attrs

changelogs/unreleased/35908-embedded-videos-not-scaled-correctly.yml

+---
+title: Fixed the scale of embedded videos to fit the page
+merge_request: 20056
+author:
+type: fixed

lib/banzai/filter/video_link_filter.rb

@@ -15,7 +15,7 @@ module Banzai
       end
 
       def extra_element_attrs
-        { width: "100%" }
+        { width: "400" }
       end
     end
   end

spec/lib/banzai/filter/video_link_filter_spec.rb

@@ -32,7 +32,7 @@ describe Banzai::Filter::VideoLinkFilter do
 
       expect(video.name).to eq 'video'
       expect(video['src']).to eq src
-      expect(video['width']).to eq "100%"
+      expect(video['width']).to eq "400"
 
       expect(paragraph.name).to eq 'p'