[BUG] String Interpolation is not supported

[mmanela]

Describe the bug

The grammar does not handle string interpolation

Requirements

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

To Reproduce

Grammar does not handle string interpolation preventing properly highlighting variables inside the string

For example this expression

$y = "hello $x[0]";

Generates a tree like this, notice the right node is just a string

(expression_statement 
        (binary_expression 
          left: (variable) 
          right: (string))) 

Expected behavior

I expect to be able to highlight variables inside of a string