Highlight CI variables ${{ }} even when inside strings

[Svalorzen]

The ${{ and }} symbols are correctly highlighted, but not when in a string. It would be nice to easily detect when a string contains a workflow variable by always adding colors for those symbols (and perhaps de-coloring the text between them).

Example:

env:
    CONFIG_VALUE: "matrix_os=${{ matrix.os == 'Windows' || '' }}"

[yasuhiroki]

@Svalorzen

In my Vim, ${{ }} are highlighted when in string.

Could you share what you see on your end?