Update GitHub Actions - #9

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Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@11d5960a326750d5838078e36cf38b85af677262, actions/setup-java@cf277c60eb25467037889841efdb72551f06f6c3, gradle/actions/setup-gradle@748248ddd2a24f49513d8f472f81c3a07d4d50e1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/