Update module github.com/stretchr/testify to v1.12.1 - #57

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4.2.2, actions/setup-go@v3, shogo82148/actions-goveralls@v1.9.0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/