Fix #21492 Add missing WebP hint in avatar/header localizations (#22395)

config/locales/simple_form.en.yml

@@ -39,14 +39,14 @@ en:
         text: You can only appeal a strike once
       defaults:
         autofollow: People who sign up through the invite will automatically follow you
-        avatar: PNG, GIF or JPG. At most %{size}. Will be downscaled to %{dimensions}px
+        avatar: WEBP, PNG, GIF or JPG. At most %{size}. Will be downscaled to %{dimensions}px
         bot: Signal to others that the account mainly performs automated actions and might not be monitored
         context: One or multiple contexts where the filter should apply
         current_password: For security purposes please enter the password of the current account
         current_username: To confirm, please enter the username of the current account
         digest: Only sent after a long period of inactivity and only if you have received any personal messages in your absence
         email: You will be sent a confirmation e-mail
-        header: PNG, GIF or JPG. At most %{size}. Will be downscaled to %{dimensions}px
+        header: WEBP, PNG, GIF or JPG. At most %{size}. Will be downscaled to %{dimensions}px
         inbox_url: Copy the URL from the frontpage of the relay you want to use
         irreversible: Filtered posts will disappear irreversibly, even if filter is later removed
         locale: The language of the user interface, e-mails and push notifications