Allow enforcing all GHA expressions are wrapped in ${{}}

[omus]

GitHub Action expressions typically need to take the form of ${{ <expression> }}. There is an exception to this rule with if clauses are where ${{ }} is optional. I've found it to be easier to read to always include the ${{ }} in if clauses to make it obvious that an expression is used.

Would it be possible to add this as a linting check? Probably this could be optional.