Add Unified label to labeler configuration

Author: hvitved

.github/labeler.yml

@@ -38,6 +38,10 @@ Swift:
   - swift/**/*
   - change-notes/**/*swift*
 
+Unified:
+  - unified/**/*
+  - change-notes/**/*unified*
+
 Actions:
   - actions/**/*
   - change-notes/**/*actions*