1. Open attached project
2. Search for Prefabs (click on All Prefabs or t:Prefab in search bar)
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You will see two prefabs from Packages folder
3. Open "DataPrivacyButton" prefab from Analytics package in Prefab mode
4. Make some changes (e.g. delete one of the components) and save
==>
ArgumentException: Saving Prefab to immutable folder is not allowed: 'Packages/com.unity.analytics/DataPrivacy/DataPrivacyButton.prefab'
UnityEditor.PrefabUtility.SavePrefab (UnityEngine.GameObject inputObject, System.String path, UnityEditor.ReplacePrefabOptions replaceOptions, UnityEditor.PrefabUtility+PrefabCreationFlags creationFlags, System.Boolean& success) (at C:/UnitySource/Trunk/Editor/Mono/Prefabs/PrefabUtility.bindings.cs:191)
UnityEditor.PrefabUtility.SaveAsPrefabAsset (UnityEngine.GameObject instanceRoot, System.String assetPath, System.Boolean& success) (at C:/UnitySource/Trunk/Editor/Mono/Prefabs/PrefabUtility.cs:1204)

Expected: The save functionality for immutable prefab in Prefab mode should be disabled