Bump github.com/hashicorp/memberlist from 0.5.4 to 0.6.0 - #56

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: workflow/nix-shell-action@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/