Dictionary unpacking causes compilation assertion error

``` python
A = {"a": 1, "b": 2, "c": 3}
B = {**A}
```

```
Assert failed: dictionary items are invalid
Expression: t && t->size() == 2
Source: /Users/runner/work/codon/codon/codon/parser/ast/expr.cpp:234
[1] 19635 abort codon run test_static.py
```