Updating warning for clarity on risk case (#31490)

Co-authored-by: Sophie <29382425+sophietheking@users.noreply.github.com>
Co-authored-by: Sophie <sophietheking@github.com>

data/reusables/actions/hosted-runner-security.md

@@ -1,3 +1 @@
-We recommend that you only use {% data variables.actions.hosted_runner %}s with private repositories:
+If you are using a Fixed IP range, we recommend that you only use {% data variables.actions.hosted_runner %}s with private repositories. Forks of your repository can potentially run dangerous code on your {% data variables.actions.hosted_runner %} by creating a pull request that executes the code in a workflow.
-- Forks of your repository can potentially run dangerous code on your {% data variables.actions.hosted_runner %} by creating a pull request that executes the code in a workflow.
-- You could incur unexpected costs if you allow forked repositories to run jobs on your {% data variables.actions.hosted_runner %}s.