fix(rewards): guard BeginBlocker against clock regression - #361

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4.2.0, actions/checkout@v4, actions/setup-go@v5, actions/upload-artifact@v4, codecov/codecov-action@v4, technote-space/get-diff-action@v6.1.2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/