docs/data/reusables/actions/expression-syntax-if.md

When you use expressions in an if conditional, you can, optionally, omit the {% raw %}${{ }}{% endraw %} expression syntax because {% data variables.product.prodname_actions %} automatically evaluates the if conditional as an expression. However, this exception does not apply everywhere.

You must always use the {% raw %}${{ }}{% endraw %} expression syntax or escape with '', "", or () when the expression starts with !, since ! is reserved notation in YAML format. For example:

{% raw %}

if: ${{ ! startsWith(github.ref, 'refs/tags/') }}

{% endraw %}