Test foreign accounts can't write to the native account

[PhilippGackstatter]

What should be done?

Afaict, we don't have a test that ensures that foreign accounts can't write to the native account the transaction is executed against. We should consider adding a test to make sure the kernel aborts if an attempt is made.

How should it be done?

Add a new FPI test. Details tbd.

When is this task done?

When a test with the above scenario results in the expected error during tx execution.

Additional context

Follow-up from #918.