Merge branch 'package-update-preparation'

Packages/manifest.json

     "com.unity.textmeshpro": "3.0.0-preview.1",
     "com.unity.timeline": "1.2.6",
     "com.unity.ugui": "1.0.0",
-    "com.unity.ui": "1.0.0-preview.3",
+    "com.unity.ui": "1.0.0-preview.6",
     "com.unity.ui.builder": "1.0.0-preview.3",
     "com.unity.vectorgraphics": "2.0.0-preview.12",
     "com.unity.modules.ai": "1.0.0",

Packages/packages-lock.json

       }
     },
     "com.unity.ui": {
-      "version": "1.0.0-preview.3",
+      "version": "1.0.0-preview.6",
       "depth": 0,
       "source": "registry",
       "dependencies": {