Update setting-up-a-trial-of-github-advanced-security.md (#56128)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Sunbrye Ly <56200261+sunbrye@users.noreply.github.com>

Author: 3 people

content/billing/managing-billing-for-your-products/managing-billing-for-github-advanced-security/setting-up-a-trial-of-github-advanced-security.md

@@ -22,6 +22,7 @@ To set up a trial of {% data variables.product.prodname_GHAS %} using this metho
 1. Be an owner of an enterprise account. See [AUTOTITLE](/enterprise-cloud@latest/admin/overview/about-enterprise-accounts).
 1. Pay by credit card or PayPal.
 1. Have not previously purchased or had a trial of {% data variables.product.prodname_GHAS %}.
+1. You must not use metered billing for {% data variables.product.prodname_GHAS %}.
 
 > [!TIP]
 > * **No enterprise account?** Start a trial of {% data variables.product.prodname_ghe_cloud %} with {% data variables.product.prodname_GHAS %}. See [AUTOTITLE](/enterprise-cloud@latest/admin/overview/setting-up-a-trial-of-github-enterprise-cloud).