Setup release/1.6 branch to sync to the internal mirror (#4384)

build/WindowsAppSDK-SyncMirroredRepository.yml

@@ -4,9 +4,9 @@ parameters:
   type: object
   default:
     main: main
-    release/1.3-stable: release/1.3-stable
     release/1.4-stable: release/1.4-stable
     release/1.5-stable: release/1.5-stable
+    release/1.6-stable: release/1.6-stable
 
 jobs:
 - job: SyncMirror