Remove advice about Actions if conditional operators

[lucascosti]

Why:

Closes #8700

What's being changed:

Remove advice about Actions if conditional operators. if conditions don't need to be enclosed in ${{ }}. Our examples still show ${{ }} because it helps avoid yaml escaping issues.

Stage preview: https://docs-8786--lucascosti-patch-1.herokuapp.com/en/actions/reference/context-and-expression-syntax-for-github-actions#about-contexts-and-expressions

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Writer impact (This section is for GitHub staff members only):

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[martin389]

Looks good to me 👍

[github-actions]

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