Tag Windows screenshots with new environment attribute

appstream now officially supports an environment attribute for screenshots.

org.kde.neochat.appdata.xml

@@ -283,7 +283,7 @@ to provide a convergent experience across multiple platforms.</p>
     <screenshot type="default">
       <image>https://cdn.kde.org/screenshots/neochat/application.png</image>
     </screenshot>
-    <screenshot x-kde-os="windows">
+    <screenshot environment="windows" x-kde-os="windows">
       <image>https://cdn.kde.org/screenshots/neochat/NeoChat-Windows-Timeline.png</image>
       <caption>Main view with room list, chat, and room information</caption>
       <caption xml:lang="ar">العرض الرئيسة مع قائمة الغرف والدردشات و معلومات الغرفة</caption>
@@ -310,7 +310,7 @@ to provide a convergent experience across multiple platforms.</p>
       <caption xml:lang="uk">Головна панель із списком кімнат, спілкуванням та даними щодо кімнати</caption>
       <caption xml:lang="x-test">xxMain view with room list, chat, and room informationxx</caption>
     </screenshot>
-    <screenshot x-kde-os="windows">
+    <screenshot environment="windows" x-kde-os="windows">
       <image>https://cdn.kde.org/screenshots/neochat/NeoChat-Windows-Login.png</image>
       <caption>Login screen</caption>
       <caption xml:lang="ar">شاشة الدخول</caption>