Modifying a nested array is not picked up by sync.

Given the schema:
```edgeql
type Foo {
val: tuple>;
};
```

the following code fails the assertion
```py
foo = default.Foo(val = ("x", [1, 2, 3]))
self.client.save(foo)

foo.val[1][0] = 9
self.client.sync(foo)

assert foo.val == ("x", [9, 2, 3]) # fails
```

See tests `test_model_sync_single_prop_04`