change lang to label

lang has to be BCP 47 standard. Using label also can let video.js know there are 2 audio tracks.

src/invidious/routes/api/manifest.cr

@@ -61,7 +61,7 @@ module Invidious::Routes::API::Manifest
             next if mime_streams.empty?
 
             mime_streams.each do |fmt|
-              xml.element("AdaptationSet", id: i, mimeType: mime_type, startWithSAP: 1, subsegmentAlignment: true, lang: i.to_s) do
+              xml.element("AdaptationSet", id: i, mimeType: mime_type, startWithSAP: 1, subsegmentAlignment: true, label: i.to_s) do
                 # OTF streams aren't supported yet (See https://github.com/TeamNewPipe/NewPipe/issues/2415)
                 next if !(fmt.has_key?("indexRange") && fmt.has_key?("initRange"))