chore: bump thiserror from 2.0.20 to 2.0.21 - #14

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: rustsec/audit-check@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/