To reproduce:

1. Open attached project.
2. Run editor test named: Component_Matrix4x4ValuesChanged_AssetHasChanges

Crash!

Tested on 2021.2.0a20, based on trunk 496d0fdd0316 revision

Stacktrace:
0x0000022457e5e7b6 (Mono JIT Code) (wrapper managed-to-native) System.Buffer:InternalMemcpy (byte*,byte*,int)
0x000002245971830b (Mono JIT Code) System.Buffer:Memcpy (byte*,byte*,int)
0x0000022457e5e683 (Mono JIT Code) string:memcpy (byte*,byte*,int)
0x00000224a256379b (Mono JIT Code) [SavePrefabComponentTest.cs:49] SavePrefabComponentTest:Component_Matrix4x4ValuesChanged_AssetHasChanges ()

Before the crash error is printed:

Can't add script behaviour MatrixHolderComponent because it is an editor script. To attach a script it needs to be outside the 'Editor' folder

UnityEngine.GameObject:AddComponent (System.Type) (at C:/unity4/Runtime/Export/Scripting/GameObject.bindings.cs:235)
UnityEngine.GameObject:.ctor (string,System.Type[]) (at C:/unity4/Runtime/Export/Scripting/GameObject.bindings.cs:379)
SavePrefabComponentTest:Component_Matrix4x4ValuesChanged_AssetHasChanges () (at Assets/Editor/SavePrefab/SavePrefabComponentTest.cs:46)