[JENKINS:SECURITY-1295-2] Sandbox Bypass via CSRF in Warnings Next Generation Plugin

Warnings Next Generation Plugin has a form validation HTTP endpoint used to validate a Groovy script through compilation, which was not subject to sandbox protection.
The endpoint checked for the Overall/RunScripts permission, but did not require POST requests, so it was vulnerable to cross-site request forgery (CSRF).
This allowed attackers to execute arbitrary code on the Jenkins controller by applying AST transforming annotations such as @Grab to source code elements.

The affected HTTP endpoint now applies a safe Groovy compiler configuration preventing the use of unsafe AST transforming annotations.
Additionally, the form validation HTTP endpoint now requires that requests be sent via POST to prevent CSRF.