Fix syntax highlighting for `def` and `final` within gstring

Consider the following:
```groovy
def str = "prefix ${def x;final y;} suffix"
```

`def` and `final` are missing keyword coloration.

![image](https://user-images.githubusercontent.com/18193802/212098294-b3c2e887-8d5f-484e-9b97-96b566d367a9.png)