fix(rulesets): duplicated-entry-in-enum - support null values - #2960

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4.3.0, browser-actions/setup-chrome@v1.2.0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/