Enables dotnet group for AppStream variant

Also adds guest-agents group for Extras variant.

variants.xml

@@ -65,7 +65,7 @@
       <group default="false">desktop-debugging</group>
       <group default="false">development</group>
       <group default="false">dns-server</group>
-<!--      <group default="false">dotnet</group>-->
+      <group default="false">dotnet</group>
       <group default="false">emacs</group>
       <group default="false">file-server</group>
       <group default="false">fonts</group>
@@ -186,5 +186,8 @@
     <arches>
       <arch>x86_64</arch>
     </arches>
+    <groups>
+      <group default="false">guest-agents</group>
+    </groups>
   </variant>
 </variants>