fix: fix comments html rendering (#5862)

Now the structure no longer has an array of author thumbnails, is a
single URL:

```json
"author": {
    "channelId": "UCiLGHgWdQvfl1G8BPgcO55w",
    "displayName": "@uber_nerd-l7r",
    "avatarThumbnailUrl": "https://yt3.ggpht.com/ee1_iFgiBvgKHUr3r0_qUVqUpGKhDZaePYq8Q4tIsyVS9L1oRHHJLcHtXrSxyS63AmvldKicbw=s88-c-k-c0x00ffffff-no-rj",
    "isVerified": false,
    "isCurrentUser": false,
    "isCreator": false,
```

src/invidious/comments/youtube.cr

@@ -155,17 +155,7 @@ module Invidious::Comments
                     json.field "authorUrl", "/channel/#{comment_author["channelId"].as_s}"
                     json.field "author", comment_author["displayName"].as_s
                     json.field "verified", comment_author["isVerified"].as_bool
-                    json.field "authorThumbnails" do
-                      json.array do
-                        comment_mutation.dig?("payload", "commentEntityPayload", "avatar", "image", "sources").try &.as_a.each do |thumbnail|
-                          json.object do
-                            json.field "url", thumbnail["url"]
-                            json.field "width", thumbnail["width"]
-                            json.field "height", thumbnail["height"]
-                          end
-                        end
-                      end
-                    end
+                    json.field "authorThumbnail", comment_author["avatarThumbnailUrl"].as_s
 
                     json.field "authorIsChannelOwner", comment_author["isCreator"].as_bool
                     json.field "isSponsor", (comment_author["sponsorBadgeUrl"]? != nil)

src/invidious/frontend/comments_youtube.cr

@@ -44,7 +44,7 @@ module Invidious::Frontend::Comments
         end
 
         if !thin_mode
-          author_thumbnail = "/ggpht#{URI.parse(child["authorThumbnails"][-1]["url"].as_s).request_target}"
+          author_thumbnail = "/ggpht#{URI.parse(child["authorThumbnail"].as_s).request_target}"
         else
           author_thumbnail = ""
         end